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	$87.86	4.117%	$91.4772	$91.48	$91.50	$91.50
Purchase #2	$77.98	6.632%	$83.1516	$83.15	$83.15	$83.20
Purchase #3	$230.80	5.774%	$244.1264	$244.13	$244.15	$244.10
Purchase #4	$206.53	4.767%	$216.3753	$216.38	$216.40	$216.40
Purchase #5	$107.38	3.645%	$111.294	$111.29	$111.30	$111.30
Purchase #6	$15.72	13.218%	$17.7979	$17.80	$17.80	$17.80
Purchase #7	$50.35	12.540%	$56.6639	$56.66	$56.65	$56.70
7 purchase totals =	$776.62		$820.8863	$820.89	$820.95	$821.00