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	$166.48	7.667%	$179.244	$179.24	$179.25	$179.20
Purchase #2	$125.72	9.590%	$137.7765	$137.78	$137.80	$137.80
Purchase #3	$29.62	9.255%	$32.3613	$32.36	$32.35	$32.40
Purchase #4	$24.93	6.802%	$26.6257	$26.63	$26.65	$26.60
Purchase #5	$132.91	7.711%	$143.1587	$143.16	$143.15	$143.20
Purchase #6	$95.89	3.719%	$99.4561	$99.46	$99.45	$99.50
Purchase #7	$117.43	9.650%	$128.762	$128.76	$128.75	$128.80
7 purchase totals =	$692.98		$747.3843	$747.39	$747.40	$747.50