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	$227.66	13.426%	$258.2256	$258.23	$258.25	$258.20
Purchase #2	$108.77	10.815%	$120.5335	$120.53	$120.55	$120.50
Purchase #3	$226.32	12.850%	$255.4021	$255.40	$255.40	$255.40
Purchase #4	$26.39	13.296%	$29.8988	$29.90	$29.90	$29.90
Purchase #5	$41.78	11.130%	$46.4301	$46.43	$46.45	$46.40
Purchase #6	$119.95	9.123%	$130.893	$130.89	$130.90	$130.90
Purchase #7	$199.74	12.103%	$223.9145	$223.91	$223.90	$223.90
7 purchase totals =	$950.61		$1,065.2976	$1,065.29	$1,065.35	$1,065.20