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	$235.39	8.484%	$255.3605	$255.36	$255.35	$255.40
Purchase #2	$139.41	4.452%	$145.6165	$145.62	$145.60	$145.60
Purchase #3	$146.37	7.516%	$157.3712	$157.37	$157.35	$157.40
Purchase #4	$175.80	5.562%	$185.578	$185.58	$185.60	$185.60
Purchase #5	$126.44	11.660%	$141.1829	$141.18	$141.20	$141.20
Purchase #6	$246.36	7.482%	$264.7927	$264.79	$264.80	$264.80
Purchase #7	$20.50	10.272%	$22.6058	$22.61	$22.60	$22.60
7 purchase totals =	$1,090.27		$1,172.5076	$1,172.51	$1,172.50	$1,172.60