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	$74.25	8.112%	$80.2732	$80.27	$80.25	$80.30
Purchase #2	$93.73	7.444%	$100.7073	$100.71	$100.70	$100.70
Purchase #3	$5.83	3.622%	$6.0412	$6.04	$6.05	$6.00
Purchase #4	$43.67	11.422%	$48.658	$48.66	$48.65	$48.70
Purchase #5	$61.86	9.806%	$67.926	$67.93	$67.95	$67.90
Purchase #6	$143.54	6.549%	$152.9404	$152.94	$152.95	$152.90
Purchase #7	$183.67	12.413%	$206.469	$206.47	$206.45	$206.50
7 purchase totals =	$606.55		$663.0151	$663.02	$663.00	$663.00