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	$35.49	11.761%	$39.664	$39.66	$39.65	$39.70
Purchase #2	$199.89	12.663%	$225.2021	$225.20	$225.20	$225.20
Purchase #3	$244.51	12.665%	$275.4772	$275.48	$275.50	$275.50
Purchase #4	$137.35	10.430%	$151.6756	$151.68	$151.70	$151.70
Purchase #5	$41.46	13.289%	$46.9696	$46.97	$46.95	$47.00
Purchase #6	$72.81	7.127%	$77.9992	$78.00	$78.00	$78.00
Purchase #7	$245.38	5.435%	$258.7164	$258.72	$258.70	$258.70
7 purchase totals =	$976.89		$1,075.7041	$1,075.71	$1,075.70	$1,075.80