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	$106.43	13.197%	$120.4756	$120.48	$120.50	$120.50
Purchase #2	$192.77	8.723%	$209.5853	$209.59	$209.60	$209.60
Purchase #3	$149.60	5.615%	$158	$158.00	$158.00	$158.00
Purchase #4	$216.59	7.200%	$232.1845	$232.18	$232.20	$232.20
Purchase #5	$185.98	5.665%	$196.5158	$196.52	$196.50	$196.50
Purchase #6	$13.46	12.413%	$15.1308	$15.13	$15.15	$15.10
Purchase #7	$129.85	12.352%	$145.8891	$145.89	$145.90	$145.90
7 purchase totals =	$994.68		$1,077.7811	$1,077.79	$1,077.85	$1,077.80