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	$61.91	3.391%	$64.0094	$64.01	$64.00	$64.00
Purchase #2	$41.83	8.519%	$45.3935	$45.39	$45.40	$45.40
Purchase #3	$33.46	13.402%	$37.9443	$37.94	$37.95	$37.90
Purchase #4	$87.47	9.569%	$95.84	$95.84	$95.85	$95.80
Purchase #5	$146.77	12.504%	$165.1221	$165.12	$165.10	$165.10
Purchase #6	$28.54	4.869%	$29.9296	$29.93	$29.95	$29.90
Purchase #7	$34.55	7.662%	$37.1972	$37.20	$37.20	$37.20
7 purchase totals =	$434.53		$475.4361	$475.43	$475.45	$475.30