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	$40.38	4.325%	$42.1264	$42.13	$42.15	$42.10
Purchase #2	$72.35	8.486%	$78.4896	$78.49	$78.50	$78.50
Purchase #3	$221.64	7.837%	$239.0099	$239.01	$239.00	$239.00
Purchase #4	$228.73	3.117%	$235.8595	$235.86	$235.85	$235.90
Purchase #5	$230.59	11.168%	$256.3423	$256.34	$256.35	$256.30
Purchase #6	$51.65	8.119%	$55.8435	$55.84	$55.85	$55.80
Purchase #7	$214.39	13.726%	$243.8172	$243.82	$243.80	$243.80
7 purchase totals =	$1,059.73		$1,151.4884	$1,151.49	$1,151.50	$1,151.40