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	$6.83	9.695%	$7.4922	$7.49	$7.50	$7.50
Purchase #2	$22.55	9.592%	$24.713	$24.71	$24.70	$24.70
Purchase #3	$188.69	4.315%	$196.832	$196.83	$196.85	$196.80
Purchase #4	$79.28	12.733%	$89.3747	$89.37	$89.35	$89.40
Purchase #5	$95.88	7.179%	$102.7632	$102.76	$102.75	$102.80
Purchase #6	$227.79	7.345%	$244.5212	$244.52	$244.50	$244.50
Purchase #7	$16.75	8.526%	$18.1781	$18.18	$18.20	$18.20
7 purchase totals =	$637.77		$683.8744	$683.86	$683.85	$683.90