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	$38.74	10.219%	$42.6988	$42.70	$42.70	$42.70
Purchase #2	$139.54	12.749%	$157.33	$157.33	$157.35	$157.30
Purchase #3	$53.51	11.232%	$59.5202	$59.52	$59.50	$59.50
Purchase #4	$22.61	12.618%	$25.4629	$25.46	$25.45	$25.50
Purchase #5	$202.47	8.229%	$219.1313	$219.13	$219.15	$219.10
Purchase #6	$44.53	12.795%	$50.2276	$50.23	$50.25	$50.20
Purchase #7	$134.80	10.140%	$148.4687	$148.47	$148.45	$148.50
7 purchase totals =	$636.20		$702.8395	$702.84	$702.85	$702.80