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	$207.90	8.443%	$225.453	$225.45	$225.45	$225.50
Purchase #2	$145.68	3.438%	$150.6885	$150.69	$150.70	$150.70
Purchase #3	$71.72	11.240%	$79.7813	$79.78	$79.80	$79.80
Purchase #4	$13.88	5.221%	$14.6047	$14.60	$14.60	$14.60
Purchase #5	$29.89	13.272%	$33.857	$33.86	$33.85	$33.90
Purchase #6	$72.61	9.437%	$79.4622	$79.46	$79.45	$79.50
Purchase #7	$20.91	4.568%	$21.8652	$21.87	$21.85	$21.90
7 purchase totals =	$562.59		$605.7119	$605.71	$605.70	$605.90