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	$14.81	6.375%	$15.7541	$15.75	$15.75	$15.80
Purchase #2	$78.53	13.535%	$89.159	$89.16	$89.15	$89.20
Purchase #3	$157.80	10.590%	$174.511	$174.51	$174.50	$174.50
Purchase #4	$104.70	4.489%	$109.4	$109.40	$109.40	$109.40
Purchase #5	$146.89	12.817%	$165.7169	$165.72	$165.70	$165.70
Purchase #6	$103.67	8.547%	$112.5307	$112.53	$112.55	$112.50
Purchase #7	$222.43	5.143%	$233.8696	$233.87	$233.85	$233.90
7 purchase totals =	$828.83		$900.9413	$900.94	$900.90	$901.00