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	$187.67	11.689%	$209.6067	$209.61	$209.60	$209.60
Purchase #2	$137.69	9.185%	$150.3368	$150.34	$150.35	$150.30
Purchase #3	$119.33	13.349%	$135.2594	$135.26	$135.25	$135.30
Purchase #4	$222.86	5.413%	$234.9234	$234.92	$234.90	$234.90
Purchase #5	$233.89	7.109%	$250.5172	$250.52	$250.50	$250.50
Purchase #6	$221.30	5.350%	$233.1396	$233.14	$233.15	$233.10
Purchase #7	$100.30	4.814%	$105.1284	$105.13	$105.15	$105.10
7 purchase totals =	$1,223.04		$1,318.9115	$1,318.92	$1,318.90	$1,318.80