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	$122.28	7.614%	$131.5904	$131.59	$131.60	$131.60
Purchase #2	$97.55	10.852%	$108.1361	$108.14	$108.15	$108.10
Purchase #3	$134.56	5.185%	$141.5369	$141.54	$141.55	$141.50
Purchase #4	$74.69	6.624%	$79.6375	$79.64	$79.65	$79.60
Purchase #5	$5.64	4.485%	$5.893	$5.89	$5.90	$5.90
Purchase #6	$30.74	3.336%	$31.7655	$31.77	$31.75	$31.80
Purchase #7	$103.32	7.590%	$111.162	$111.16	$111.15	$111.20
7 purchase totals =	$568.78		$609.7214	$609.73	$609.75	$609.70