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	$108.39	10.551%	$119.8262	$119.83	$119.85	$119.80
Purchase #2	$227.56	5.413%	$239.8778	$239.88	$239.90	$239.90
Purchase #3	$118.25	8.371%	$128.1487	$128.15	$128.15	$128.10
Purchase #4	$135.45	11.561%	$151.1094	$151.11	$151.10	$151.10
Purchase #5	$56.49	10.638%	$62.4994	$62.50	$62.50	$62.50
Purchase #6	$204.29	13.223%	$231.3033	$231.30	$231.30	$231.30
Purchase #7	$63.76	11.207%	$70.9056	$70.91	$70.90	$70.90
7 purchase totals =	$914.19		$1,003.6704	$1,003.68	$1,003.70	$1,003.60