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	$248.90	13.109%	$281.5283	$281.53	$281.55	$281.50
Purchase #2	$137.94	9.603%	$151.1864	$151.19	$151.20	$151.20
Purchase #3	$34.80	12.873%	$39.2798	$39.28	$39.30	$39.30
Purchase #4	$44.66	5.578%	$47.1511	$47.15	$47.15	$47.20
Purchase #5	$20.53	13.810%	$23.3652	$23.37	$23.35	$23.40
Purchase #6	$83.79	7.306%	$89.9117	$89.91	$89.90	$89.90
Purchase #7	$40.29	4.594%	$42.1409	$42.14	$42.15	$42.10
7 purchase totals =	$610.91		$674.5634	$674.57	$674.60	$674.60