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	$18.68	11.132%	$20.7595	$20.76	$20.75	$20.80
Purchase #2	$137.75	7.679%	$148.3278	$148.33	$148.35	$148.30
Purchase #3	$49.77	8.713%	$54.1065	$54.11	$54.10	$54.10
Purchase #4	$36.36	11.338%	$40.4825	$40.48	$40.50	$40.50
Purchase #5	$152.25	12.652%	$171.5127	$171.51	$171.50	$171.50
Purchase #6	$166.39	5.520%	$175.5747	$175.57	$175.55	$175.60
Purchase #7	$60.30	12.639%	$67.9213	$67.92	$67.90	$67.90
7 purchase totals =	$621.50		$678.6850	$678.68	$678.65	$678.70