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	$199.27	9.530%	$218.2604	$218.26	$218.25	$218.30
Purchase #2	$218.72	11.381%	$243.6125	$243.61	$243.60	$243.60
Purchase #3	$60.29	3.502%	$62.4014	$62.40	$62.40	$62.40
Purchase #4	$204.84	13.262%	$232.0059	$232.01	$232.00	$232.00
Purchase #5	$84.45	5.599%	$89.1784	$89.18	$89.20	$89.20
Purchase #6	$126.45	10.173%	$139.3138	$139.31	$139.30	$139.30
Purchase #7	$25.77	10.457%	$28.4648	$28.46	$28.45	$28.50
7 purchase totals =	$919.79		$1,013.2372	$1,013.23	$1,013.20	$1,013.30