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	$70.93	8.344%	$76.8484	$76.85	$76.85	$76.80
Purchase #2	$53.74	3.809%	$55.787	$55.79	$55.80	$55.80
Purchase #3	$220.76	10.447%	$243.8228	$243.82	$243.80	$243.80
Purchase #4	$243.59	13.419%	$276.2773	$276.28	$276.30	$276.30
Purchase #5	$40.47	12.816%	$45.6566	$45.66	$45.65	$45.70
Purchase #6	$247.27	5.513%	$260.902	$260.90	$260.90	$260.90
Purchase #7	$39.34	9.407%	$43.0407	$43.04	$43.05	$43.00
7 purchase totals =	$916.10		$1,002.3348	$1,002.34	$1,002.35	$1,002.30