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	$87.75	9.211%	$95.8327	$95.83	$95.85	$95.80
Purchase #2	$104.50	7.201%	$112.025	$112.03	$112.05	$112.00
Purchase #3	$137.76	6.358%	$146.5188	$146.52	$146.50	$146.50
Purchase #4	$132.33	9.706%	$145.1739	$145.17	$145.15	$145.20
Purchase #5	$18.34	9.655%	$20.1107	$20.11	$20.10	$20.10
Purchase #6	$37.36	7.850%	$40.2928	$40.29	$40.30	$40.30
Purchase #7	$79.50	8.668%	$86.3911	$86.39	$86.40	$86.40
7 purchase totals =	$597.54		$646.3450	$646.34	$646.35	$646.30