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	$198.47	12.601%	$223.4792	$223.48	$223.50	$223.50
Purchase #2	$108.69	8.355%	$117.771	$117.77	$117.75	$117.80
Purchase #3	$72.34	10.385%	$79.8525	$79.85	$79.85	$79.90
Purchase #4	$204.50	9.845%	$224.633	$224.63	$224.65	$224.60
Purchase #5	$147.82	12.256%	$165.9368	$165.94	$165.95	$165.90
Purchase #6	$170.75	5.460%	$180.073	$180.07	$180.05	$180.10
Purchase #7	$77.97	5.317%	$82.1157	$82.12	$82.10	$82.10
7 purchase totals =	$980.54		$1,073.8612	$1,073.86	$1,073.85	$1,073.90