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	$37.81	12.521%	$42.5442	$42.54	$42.55	$42.50
Purchase #2	$82.28	5.471%	$86.7815	$86.78	$86.80	$86.80
Purchase #3	$11.29	12.563%	$12.7084	$12.71	$12.70	$12.70
Purchase #4	$85.81	8.508%	$93.1107	$93.11	$93.10	$93.10
Purchase #5	$36.69	10.831%	$40.6639	$40.66	$40.65	$40.70
Purchase #6	$158.31	4.489%	$165.4165	$165.42	$165.40	$165.40
Purchase #7	$52.26	9.863%	$57.4144	$57.41	$57.40	$57.40
7 purchase totals =	$464.45		$498.6396	$498.63	$498.60	$498.60