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	$28.56	13.188%	$32.3265	$32.33	$32.35	$32.30
Purchase #2	$59.29	3.636%	$61.4458	$61.45	$61.45	$61.40
Purchase #3	$78.37	4.869%	$82.1858	$82.19	$82.20	$82.20
Purchase #4	$185.75	13.197%	$210.2634	$210.26	$210.25	$210.30
Purchase #5	$199.89	10.105%	$220.0889	$220.09	$220.10	$220.10
Purchase #6	$143.37	4.576%	$149.9306	$149.93	$149.95	$149.90
Purchase #7	$81.37	8.478%	$88.2685	$88.27	$88.25	$88.30
7 purchase totals =	$776.60		$844.5095	$844.52	$844.55	$844.50