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	$53.47	12.709%	$60.2655	$60.27	$60.25	$60.30
Purchase #2	$190.48	12.832%	$214.9224	$214.92	$214.90	$214.90
Purchase #3	$93.53	8.301%	$101.2939	$101.29	$101.30	$101.30
Purchase #4	$135.45	8.362%	$146.7763	$146.78	$146.80	$146.80
Purchase #5	$79.98	12.700%	$90.1375	$90.14	$90.15	$90.10
Purchase #6	$126.90	4.791%	$132.9798	$132.98	$133.00	$133.00
Purchase #7	$90.71	13.752%	$103.1844	$103.18	$103.20	$103.20
7 purchase totals =	$770.52		$849.5598	$849.56	$849.60	$849.60