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	$205.90	10.872%	$228.2854	$228.29	$228.30	$228.30
Purchase #2	$172.59	13.588%	$196.0415	$196.04	$196.05	$196.00
Purchase #3	$211.40	7.325%	$226.8851	$226.89	$226.90	$226.90
Purchase #4	$152.82	8.500%	$165.8097	$165.81	$165.80	$165.80
Purchase #5	$18.28	13.556%	$20.758	$20.76	$20.75	$20.80
Purchase #6	$36.53	12.362%	$41.0458	$41.05	$41.05	$41.00
Purchase #7	$91.93	3.467%	$95.1172	$95.12	$95.10	$95.10
7 purchase totals =	$889.45		$973.9427	$973.96	$973.95	$973.90