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	$250.54	12.362%	$281.5118	$281.51	$281.50	$281.50
Purchase #2	$71.96	8.177%	$77.8442	$77.84	$77.85	$77.80
Purchase #3	$36.89	11.485%	$41.1268	$41.13	$41.15	$41.10
Purchase #4	$56.47	13.206%	$63.9274	$63.93	$63.95	$63.90
Purchase #5	$175.46	9.726%	$192.5252	$192.53	$192.55	$192.50
Purchase #6	$72.40	13.400%	$82.1016	$82.10	$82.10	$82.10
Purchase #7	$225.88	7.682%	$243.2321	$243.23	$243.25	$243.20
7 purchase totals =	$889.60		$982.2691	$982.27	$982.35	$982.10