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	$218.42	3.247%	$225.5121	$225.51	$225.50	$225.50
Purchase #2	$217.89	7.361%	$233.9289	$233.93	$233.95	$233.90
Purchase #3	$62.43	5.187%	$65.6682	$65.67	$65.65	$65.70
Purchase #4	$144.88	13.268%	$164.1027	$164.10	$164.10	$164.10
Purchase #5	$60.75	11.817%	$67.9288	$67.93	$67.95	$67.90
Purchase #6	$85.56	7.794%	$92.2285	$92.23	$92.25	$92.20
Purchase #7	$140.59	4.643%	$147.1176	$147.12	$147.10	$147.10
7 purchase totals =	$930.52		$996.4868	$996.49	$996.50	$996.40