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	$135.94	7.773%	$146.5066	$146.51	$146.50	$146.50
Purchase #2	$40.69	12.690%	$45.8536	$45.85	$45.85	$45.90
Purchase #3	$61.58	13.643%	$69.9814	$69.98	$70.00	$70.00
Purchase #4	$71.67	11.443%	$79.8712	$79.87	$79.85	$79.90
Purchase #5	$169.36	13.337%	$191.9475	$191.95	$191.95	$191.90
Purchase #6	$87.31	6.419%	$92.9144	$92.91	$92.90	$92.90
Purchase #7	$193.34	6.130%	$205.1917	$205.19	$205.20	$205.20
7 purchase totals =	$759.89		$832.2664	$832.26	$832.25	$832.30