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	$250.87	8.544%	$272.3043	$272.30	$272.30	$272.30
Purchase #2	$67.65	4.678%	$70.8147	$70.81	$70.80	$70.80
Purchase #3	$124.77	10.182%	$137.4741	$137.47	$137.45	$137.50
Purchase #4	$139.58	11.151%	$155.1446	$155.14	$155.15	$155.10
Purchase #5	$79.27	12.109%	$88.8688	$88.87	$88.85	$88.90
Purchase #6	$246.54	11.512%	$274.9217	$274.92	$274.90	$274.90
Purchase #7	$133.59	13.619%	$151.7836	$151.78	$151.80	$151.80
7 purchase totals =	$1,042.27		$1,151.3118	$1,151.29	$1,151.25	$1,151.30