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	$159.95	7.456%	$171.8759	$171.88	$171.90	$171.90
Purchase #2	$188.49	8.639%	$204.7737	$204.77	$204.75	$204.80
Purchase #3	$65.39	11.461%	$72.8843	$72.88	$72.90	$72.90
Purchase #4	$88.68	5.570%	$93.6195	$93.62	$93.60	$93.60
Purchase #5	$136.77	11.584%	$152.6134	$152.61	$152.60	$152.60
Purchase #6	$153.91	8.153%	$166.4583	$166.46	$166.45	$166.50
Purchase #7	$209.62	8.733%	$227.9261	$227.93	$227.95	$227.90
7 purchase totals =	$1,002.81		$1,090.1512	$1,090.15	$1,090.15	$1,090.20