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	$133.49	7.333%	$143.2788	$143.28	$143.30	$143.30
Purchase #2	$242.34	5.423%	$255.4821	$255.48	$255.50	$255.50
Purchase #3	$44.87	7.444%	$48.2101	$48.21	$48.20	$48.20
Purchase #4	$13.40	12.499%	$15.0749	$15.07	$15.05	$15.10
Purchase #5	$147.34	7.337%	$158.1503	$158.15	$158.15	$158.20
Purchase #6	$127.45	6.827%	$136.151	$136.15	$136.15	$136.20
Purchase #7	$76.61	7.363%	$82.2508	$82.25	$82.25	$82.30
7 purchase totals =	$785.50		$838.5980	$838.59	$838.60	$838.80