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	$64.53	11.343%	$71.8496	$71.85	$71.85	$71.80
Purchase #2	$142.73	5.491%	$150.5673	$150.57	$150.55	$150.60
Purchase #3	$124.49	3.153%	$128.4152	$128.42	$128.40	$128.40
Purchase #4	$203.44	13.458%	$230.819	$230.82	$230.80	$230.80
Purchase #5	$203.42	10.344%	$224.4618	$224.46	$224.45	$224.50
Purchase #6	$88.61	5.290%	$93.2975	$93.30	$93.30	$93.30
Purchase #7	$165.29	4.338%	$172.4603	$172.46	$172.45	$172.50
7 purchase totals =	$992.51		$1,071.8707	$1,071.88	$1,071.80	$1,071.90