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	$28.57	12.850%	$32.2412	$32.24	$32.25	$32.20
Purchase #2	$36.58	11.114%	$40.6455	$40.65	$40.65	$40.60
Purchase #3	$31.33	4.399%	$32.7082	$32.71	$32.70	$32.70
Purchase #4	$230.48	13.303%	$261.1408	$261.14	$261.15	$261.10
Purchase #5	$39.43	10.850%	$43.7082	$43.71	$43.70	$43.70
Purchase #6	$238.56	6.461%	$253.9734	$253.97	$253.95	$254.00
Purchase #7	$50.48	12.133%	$56.6047	$56.60	$56.60	$56.60
7 purchase totals =	$655.43		$721.0220	$721.02	$721.00	$720.90