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	$34.56	8.380%	$37.4561	$37.46	$37.45	$37.50
Purchase #2	$98.35	10.228%	$108.4092	$108.41	$108.40	$108.40
Purchase #3	$126.61	13.331%	$143.4884	$143.49	$143.50	$143.50
Purchase #4	$57.42	7.582%	$61.7736	$61.77	$61.75	$61.80
Purchase #5	$72.55	3.261%	$74.9159	$74.92	$74.90	$74.90
Purchase #6	$85.85	5.378%	$90.467	$90.47	$90.45	$90.50
Purchase #7	$11.80	13.661%	$13.412	$13.41	$13.40	$13.40
7 purchase totals =	$487.14		$529.9222	$529.93	$529.85	$530.00