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	$10.28	13.131%	$11.6299	$11.63	$11.65	$11.60
Purchase #2	$51.28	8.349%	$55.5614	$55.56	$55.55	$55.60
Purchase #3	$89.63	10.779%	$99.2912	$99.29	$99.30	$99.30
Purchase #4	$37.74	13.836%	$42.9617	$42.96	$42.95	$43.00
Purchase #5	$190.80	4.741%	$199.8458	$199.85	$199.85	$199.80
Purchase #6	$141.56	7.639%	$152.3738	$152.37	$152.35	$152.40
Purchase #7	$66.75	11.472%	$74.4076	$74.41	$74.40	$74.40
7 purchase totals =	$588.04		$636.0714	$636.07	$636.05	$636.10