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	$240.83	3.221%	$248.5871	$248.59	$248.60	$248.60
Purchase #2	$199.76	12.203%	$224.1367	$224.14	$224.15	$224.10
Purchase #3	$174.48	6.341%	$185.5438	$185.54	$185.55	$185.50
Purchase #4	$37.30	8.389%	$40.4291	$40.43	$40.45	$40.40
Purchase #5	$192.98	3.551%	$199.8327	$199.83	$199.85	$199.80
Purchase #6	$33.61	13.217%	$38.0522	$38.05	$38.05	$38.10
Purchase #7	$18.63	4.210%	$19.4143	$19.41	$19.40	$19.40
7 purchase totals =	$897.59		$955.9959	$955.99	$956.05	$955.90