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	$20.46	5.776%	$21.6418	$21.64	$21.65	$21.60
Purchase #2	$99.92	13.753%	$113.662	$113.66	$113.65	$113.70
Purchase #3	$131.67	5.725%	$139.2081	$139.21	$139.20	$139.20
Purchase #4	$250.29	5.657%	$264.4489	$264.45	$264.45	$264.40
Purchase #5	$174.74	12.463%	$196.5178	$196.52	$196.50	$196.50
Purchase #6	$54.90	11.768%	$61.3606	$61.36	$61.35	$61.40
Purchase #7	$139.94	10.207%	$154.2237	$154.22	$154.20	$154.20
7 purchase totals =	$871.92		$951.0629	$951.06	$951.00	$951.00