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	$24.77	11.609%	$27.6455	$27.65	$27.65	$27.60
Purchase #2	$197.62	6.797%	$211.0522	$211.05	$211.05	$211.10
Purchase #3	$56.28	5.606%	$59.4351	$59.44	$59.45	$59.40
Purchase #4	$36.33	11.354%	$40.4549	$40.45	$40.45	$40.50
Purchase #5	$166.63	3.304%	$172.1355	$172.14	$172.15	$172.10
Purchase #6	$110.37	6.545%	$117.5937	$117.59	$117.60	$117.60
Purchase #7	$112.77	11.345%	$125.5638	$125.56	$125.55	$125.60
7 purchase totals =	$704.77		$753.8807	$753.88	$753.90	$753.90