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	$234.82	7.826%	$253.197	$253.20	$253.20	$253.20
Purchase #2	$36.66	10.152%	$40.3817	$40.38	$40.40	$40.40
Purchase #3	$129.44	8.434%	$140.357	$140.36	$140.35	$140.40
Purchase #4	$92.71	8.289%	$100.3947	$100.39	$100.40	$100.40
Purchase #5	$151.71	7.251%	$162.7105	$162.71	$162.70	$162.70
Purchase #6	$208.45	4.523%	$217.8782	$217.88	$217.90	$217.90
Purchase #7	$37.93	12.294%	$42.5931	$42.59	$42.60	$42.60
7 purchase totals =	$891.72		$957.5122	$957.51	$957.55	$957.60