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	$223.72	6.575%	$238.4296	$238.43	$238.45	$238.40
Purchase #2	$143.71	5.406%	$151.479	$151.48	$151.50	$151.50
Purchase #3	$39.40	3.559%	$40.8022	$40.80	$40.80	$40.80
Purchase #4	$212.73	7.543%	$228.7762	$228.78	$228.80	$228.80
Purchase #5	$141.80	5.345%	$149.3792	$149.38	$149.40	$149.40
Purchase #6	$214.70	3.619%	$222.47	$222.47	$222.45	$222.50
Purchase #7	$196.83	7.730%	$212.045	$212.05	$212.05	$212.00
7 purchase totals =	$1,172.89		$1,243.3812	$1,243.39	$1,243.45	$1,243.40