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	$146.58	6.285%	$155.7926	$155.79	$155.80	$155.80
Purchase #2	$166.71	7.113%	$178.5681	$178.57	$178.55	$178.60
Purchase #3	$90.35	5.465%	$95.2876	$95.29	$95.30	$95.30
Purchase #4	$133.48	13.481%	$151.4744	$151.47	$151.45	$151.50
Purchase #5	$146.25	3.203%	$150.9344	$150.93	$150.95	$150.90
Purchase #6	$137.59	6.254%	$146.1949	$146.19	$146.20	$146.20
Purchase #7	$30.77	9.590%	$33.7208	$33.72	$33.70	$33.70
7 purchase totals =	$851.73		$911.9728	$911.96	$911.95	$912.00