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	$54.37	8.282%	$58.8729	$58.87	$58.85	$58.90
Purchase #2	$165.90	11.532%	$185.0316	$185.03	$185.05	$185.00
Purchase #3	$98.73	11.355%	$109.9408	$109.94	$109.95	$109.90
Purchase #4	$83.78	10.749%	$92.7855	$92.79	$92.80	$92.80
Purchase #5	$130.52	12.550%	$146.9003	$146.90	$146.90	$146.90
Purchase #6	$227.36	10.460%	$251.1419	$251.14	$251.15	$251.10
Purchase #7	$153.71	3.547%	$159.1621	$159.16	$159.15	$159.20
7 purchase totals =	$914.37		$1,003.8351	$1,003.83	$1,003.85	$1,003.80