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	$37.29	7.520%	$40.0942	$40.09	$40.10	$40.10
Purchase #2	$91.34	5.822%	$96.6578	$96.66	$96.65	$96.70
Purchase #3	$225.70	4.684%	$236.2718	$236.27	$236.25	$236.30
Purchase #4	$185.40	7.561%	$199.4181	$199.42	$199.40	$199.40
Purchase #5	$102.65	8.425%	$111.2983	$111.30	$111.30	$111.30
Purchase #6	$248.46	12.392%	$279.2492	$279.25	$279.25	$279.20
Purchase #7	$139.76	8.124%	$151.1141	$151.11	$151.10	$151.10
7 purchase totals =	$1,030.60		$1,114.1035	$1,114.10	$1,114.05	$1,114.10