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	$241.73	6.105%	$256.4876	$256.49	$256.50	$256.50
Purchase #2	$90.69	8.721%	$98.5991	$98.60	$98.60	$98.60
Purchase #3	$152.64	12.142%	$171.1735	$171.17	$171.15	$171.20
Purchase #4	$139.35	13.467%	$158.1163	$158.12	$158.10	$158.10
Purchase #5	$75.38	10.258%	$83.1125	$83.11	$83.10	$83.10
Purchase #6	$161.96	8.613%	$175.9096	$175.91	$175.90	$175.90
Purchase #7	$7.62	6.584%	$8.1217	$8.12	$8.10	$8.10
7 purchase totals =	$869.37		$951.5203	$951.52	$951.45	$951.50