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	$203.76	10.182%	$224.5068	$224.51	$224.50	$224.50
Purchase #2	$34.81	8.603%	$37.8047	$37.80	$37.80	$37.80
Purchase #3	$37.68	13.579%	$42.7966	$42.80	$42.80	$42.80
Purchase #4	$188.70	5.450%	$198.9842	$198.98	$199.00	$199.00
Purchase #5	$171.66	10.738%	$190.0929	$190.09	$190.10	$190.10
Purchase #6	$97.77	7.683%	$105.2817	$105.28	$105.30	$105.30
Purchase #7	$55.41	7.729%	$59.6926	$59.69	$59.70	$59.70
7 purchase totals =	$789.79		$859.1595	$859.15	$859.20	$859.20