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	$13.92	11.532%	$15.5253	$15.53	$15.55	$15.50
Purchase #2	$145.93	3.275%	$150.7092	$150.71	$150.70	$150.70
Purchase #3	$246.39	11.346%	$274.3454	$274.35	$274.35	$274.30
Purchase #4	$237.82	3.345%	$245.7751	$245.78	$245.80	$245.80
Purchase #5	$165.45	4.666%	$173.1699	$173.17	$173.15	$173.20
Purchase #6	$172.54	5.188%	$181.4914	$181.49	$181.50	$181.50
Purchase #7	$21.75	11.186%	$24.183	$24.18	$24.20	$24.20
7 purchase totals =	$1,003.80		$1,065.1993	$1,065.21	$1,065.25	$1,065.20