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	$72.79	12.828%	$82.1275	$82.13	$82.15	$82.10
Purchase #2	$244.56	10.537%	$270.3293	$270.33	$270.35	$270.30
Purchase #3	$143.28	10.472%	$158.2843	$158.28	$158.30	$158.30
Purchase #4	$37.72	12.205%	$42.3237	$42.32	$42.30	$42.30
Purchase #5	$16.83	12.761%	$18.9777	$18.98	$19.00	$19.00
Purchase #6	$203.77	4.398%	$212.7318	$212.73	$212.75	$212.70
Purchase #7	$215.30	11.837%	$240.7851	$240.79	$240.80	$240.80
7 purchase totals =	$934.25		$1,025.5594	$1,025.56	$1,025.65	$1,025.50