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	$200.85	12.760%	$226.4785	$226.48	$226.50	$226.50
Purchase #2	$58.64	13.623%	$66.6285	$66.63	$66.65	$66.60
Purchase #3	$223.95	13.283%	$253.6973	$253.70	$253.70	$253.70
Purchase #4	$78.47	4.678%	$82.1408	$82.14	$82.15	$82.10
Purchase #5	$152.73	5.748%	$161.5089	$161.51	$161.50	$161.50
Purchase #6	$50.71	10.298%	$55.9321	$55.93	$55.95	$55.90
Purchase #7	$140.55	7.355%	$150.8875	$150.89	$150.90	$150.90
7 purchase totals =	$905.90		$997.2736	$997.28	$997.35	$997.20