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	$231.29	6.472%	$246.2591	$246.26	$246.25	$246.30
Purchase #2	$146.68	7.589%	$157.8115	$157.81	$157.80	$157.80
Purchase #3	$43.34	8.181%	$46.8856	$46.89	$46.90	$46.90
Purchase #4	$99.56	12.766%	$112.2698	$112.27	$112.25	$112.30
Purchase #5	$182.47	5.183%	$191.9274	$191.93	$191.95	$191.90
Purchase #6	$66.90	6.549%	$71.2813	$71.28	$71.30	$71.30
Purchase #7	$7.47	13.151%	$8.4524	$8.45	$8.45	$8.50
7 purchase totals =	$777.71		$834.8871	$834.89	$834.90	$835.00