Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $132.97   12.413%   $149.4756   $149.48   $149.50   $149.50  
  Purchase #2 $9.39   4.326%   $9.7962   $9.80   $9.80   $9.80  
  Purchase #3 $65.79   3.641%   $68.1854   $68.19   $68.20   $68.20  
  Purchase #4 $74.53   4.284%   $77.7229   $77.72   $77.70   $77.70  
  Purchase #5 $175.28   8.851%   $190.794   $190.79   $190.80   $190.80  
  Purchase #6 $238.94   9.714%   $262.1506   $262.15   $262.15   $262.20  
  Purchase #7 $109.60   5.249%   $115.3529   $115.35   $115.35   $115.40  
  7 purchase totals = $806.50       $873.4776   $873.48   $873.50   $873.60