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	$151.35	3.338%	$156.4021	$156.40	$156.40	$156.40
Purchase #2	$175.51	9.589%	$192.3397	$192.34	$192.35	$192.30
Purchase #3	$223.91	9.203%	$244.5164	$244.52	$244.50	$244.50
Purchase #4	$248.93	6.187%	$264.3313	$264.33	$264.35	$264.30
Purchase #5	$32.41	10.119%	$35.6896	$35.69	$35.70	$35.70
Purchase #6	$71.98	7.569%	$77.4282	$77.43	$77.45	$77.40
Purchase #7	$220.41	4.234%	$229.7422	$229.74	$229.75	$229.70
7 purchase totals =	$1,124.50		$1,200.4495	$1,200.45	$1,200.50	$1,200.30