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	$227.29	10.751%	$251.7259	$251.73	$251.75	$251.70
Purchase #2	$195.25	11.726%	$218.145	$218.15	$218.15	$218.10
Purchase #3	$56.47	8.218%	$61.1107	$61.11	$61.10	$61.10
Purchase #4	$90.35	11.109%	$100.387	$100.39	$100.40	$100.40
Purchase #5	$157.73	12.770%	$177.8721	$177.87	$177.85	$177.90
Purchase #6	$12.43	3.791%	$12.9012	$12.90	$12.90	$12.90
Purchase #7	$71.37	12.312%	$80.1571	$80.16	$80.15	$80.20
7 purchase totals =	$810.89		$902.2990	$902.31	$902.30	$902.30