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	$85.84	5.153%	$90.2633	$90.26	$90.25	$90.30
Purchase #2	$169.80	13.565%	$192.8334	$192.83	$192.85	$192.80
Purchase #3	$147.31	9.753%	$161.6771	$161.68	$161.70	$161.70
Purchase #4	$39.67	6.600%	$42.2882	$42.29	$42.30	$42.30
Purchase #5	$84.62	4.346%	$88.2976	$88.30	$88.30	$88.30
Purchase #6	$36.47	6.669%	$38.9022	$38.90	$38.90	$38.90
Purchase #7	$28.64	13.315%	$32.4534	$32.45	$32.45	$32.50
7 purchase totals =	$592.35		$646.7152	$646.71	$646.75	$646.80