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	$96.57	12.341%	$108.4877	$108.49	$108.50	$108.50
Purchase #2	$166.87	10.453%	$184.3129	$184.31	$184.30	$184.30
Purchase #3	$122.33	4.582%	$127.9352	$127.94	$127.95	$127.90
Purchase #4	$64.52	12.863%	$72.8192	$72.82	$72.80	$72.80
Purchase #5	$230.89	5.785%	$244.247	$244.25	$244.25	$244.20
Purchase #6	$26.33	11.726%	$29.4175	$29.42	$29.40	$29.40
Purchase #7	$116.96	7.133%	$125.3028	$125.30	$125.30	$125.30
7 purchase totals =	$824.47		$892.5223	$892.53	$892.50	$892.40