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	$23.42	6.141%	$24.8582	$24.86	$24.85	$24.90
Purchase #2	$59.74	3.873%	$62.0537	$62.05	$62.05	$62.10
Purchase #3	$59.55	3.417%	$61.5848	$61.58	$61.60	$61.60
Purchase #4	$191.95	13.653%	$218.1569	$218.16	$218.15	$218.20
Purchase #5	$42.40	10.338%	$46.7833	$46.78	$46.80	$46.80
Purchase #6	$13.34	4.111%	$13.8884	$13.89	$13.90	$13.90
Purchase #7	$225.29	13.540%	$255.7943	$255.79	$255.80	$255.80
7 purchase totals =	$615.69		$683.1196	$683.11	$683.15	$683.30