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	$89.50	12.476%	$100.666	$100.67	$100.65	$100.70
Purchase #2	$125.50	11.465%	$139.8886	$139.89	$139.90	$139.90
Purchase #3	$143.81	12.148%	$161.28	$161.28	$161.30	$161.30
Purchase #4	$44.26	7.661%	$47.6508	$47.65	$47.65	$47.70
Purchase #5	$6.70	7.853%	$7.2262	$7.23	$7.25	$7.20
Purchase #6	$27.85	5.184%	$29.2937	$29.29	$29.30	$29.30
Purchase #7	$44.51	4.272%	$46.4115	$46.41	$46.40	$46.40
7 purchase totals =	$482.13		$532.4168	$532.42	$532.45	$532.50