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	$241.42	7.108%	$258.5801	$258.58	$258.60	$258.60
Purchase #2	$211.73	8.341%	$229.3904	$229.39	$229.40	$229.40
Purchase #3	$100.90	4.622%	$105.5636	$105.56	$105.55	$105.60
Purchase #4	$112.88	10.272%	$124.475	$124.48	$124.50	$124.50
Purchase #5	$33.85	10.611%	$37.4418	$37.44	$37.45	$37.40
Purchase #6	$101.96	3.160%	$105.1819	$105.18	$105.20	$105.20
Purchase #7	$89.52	11.395%	$99.7208	$99.72	$99.70	$99.70
7 purchase totals =	$892.26		$960.3536	$960.35	$960.40	$960.40