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	$72.47	8.645%	$78.735	$78.74	$78.75	$78.70
Purchase #2	$226.48	4.306%	$236.2322	$236.23	$236.25	$236.20
Purchase #3	$165.42	4.794%	$173.3502	$173.35	$173.35	$173.40
Purchase #4	$223.47	13.804%	$254.3178	$254.32	$254.30	$254.30
Purchase #5	$151.95	3.799%	$157.7226	$157.72	$157.70	$157.70
Purchase #6	$88.54	6.690%	$94.4633	$94.46	$94.45	$94.50
Purchase #7	$153.79	12.785%	$173.4521	$173.45	$173.45	$173.50
7 purchase totals =	$1,082.12		$1,168.2732	$1,168.27	$1,168.25	$1,168.30