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	$92.74	8.316%	$100.4523	$100.45	$100.45	$100.50
Purchase #2	$185.37	13.192%	$209.824	$209.82	$209.80	$209.80
Purchase #3	$179.52	5.552%	$189.487	$189.49	$189.50	$189.50
Purchase #4	$25.25	10.616%	$27.9305	$27.93	$27.95	$27.90
Purchase #5	$147.34	12.203%	$165.3199	$165.32	$165.30	$165.30
Purchase #6	$124.99	12.573%	$140.705	$140.71	$140.70	$140.70
Purchase #7	$19.90	10.168%	$21.9234	$21.92	$21.90	$21.90
7 purchase totals =	$775.11		$855.6421	$855.64	$855.60	$855.60