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	$245.57	10.234%	$270.7016	$270.70	$270.70	$270.70
Purchase #2	$18.37	5.670%	$19.4116	$19.41	$19.40	$19.40
Purchase #3	$204.68	11.472%	$228.1609	$228.16	$228.15	$228.20
Purchase #4	$89.89	13.255%	$101.8049	$101.80	$101.80	$101.80
Purchase #5	$211.67	5.104%	$222.4736	$222.47	$222.45	$222.50
Purchase #6	$238.86	7.552%	$256.8987	$256.90	$256.90	$256.90
Purchase #7	$212.86	4.263%	$221.9342	$221.93	$221.95	$221.90
7 purchase totals =	$1,221.90		$1,321.3855	$1,321.37	$1,321.35	$1,321.40