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	$75.50	6.443%	$80.3645	$80.36	$80.35	$80.40
Purchase #2	$52.86	3.217%	$54.5605	$54.56	$54.55	$54.60
Purchase #3	$169.87	3.504%	$175.8222	$175.82	$175.80	$175.80
Purchase #4	$127.48	12.445%	$143.3449	$143.34	$143.35	$143.30
Purchase #5	$10.88	4.556%	$11.3757	$11.38	$11.40	$11.40
Purchase #6	$30.44	6.451%	$32.4037	$32.40	$32.40	$32.40
Purchase #7	$30.48	10.634%	$33.7212	$33.72	$33.70	$33.70
7 purchase totals =	$497.51		$531.5927	$531.58	$531.55	$531.60