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	$86.36	13.848%	$98.3191	$98.32	$98.30	$98.30
Purchase #2	$91.89	12.820%	$103.6703	$103.67	$103.65	$103.70
Purchase #3	$243.52	6.716%	$259.8748	$259.87	$259.85	$259.90
Purchase #4	$196.73	7.168%	$210.8316	$210.83	$210.85	$210.80
Purchase #5	$65.69	7.664%	$70.7245	$70.72	$70.70	$70.70
Purchase #6	$56.30	8.377%	$61.0163	$61.02	$61.00	$61.00
Purchase #7	$144.35	5.160%	$151.7985	$151.80	$151.80	$151.80
7 purchase totals =	$884.84		$956.2351	$956.23	$956.15	$956.20