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	$39.28	7.208%	$42.1113	$42.11	$42.10	$42.10
Purchase #2	$67.33	6.502%	$71.7078	$71.71	$71.70	$71.70
Purchase #3	$85.41	10.457%	$94.3413	$94.34	$94.35	$94.30
Purchase #4	$238.70	7.143%	$255.7503	$255.75	$255.75	$255.80
Purchase #5	$100.67	11.867%	$112.6165	$112.62	$112.60	$112.60
Purchase #6	$44.94	3.786%	$46.6414	$46.64	$46.65	$46.60
Purchase #7	$107.62	11.456%	$119.9489	$119.95	$119.95	$119.90
7 purchase totals =	$683.95		$743.1175	$743.12	$743.10	$743.00