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	$50.55	8.358%	$54.775	$54.78	$54.80	$54.80
Purchase #2	$131.67	11.310%	$146.5619	$146.56	$146.55	$146.60
Purchase #3	$38.95	9.802%	$42.7679	$42.77	$42.75	$42.80
Purchase #4	$73.97	4.348%	$77.1862	$77.19	$77.20	$77.20
Purchase #5	$172.74	7.621%	$185.9045	$185.90	$185.90	$185.90
Purchase #6	$67.31	7.166%	$72.1334	$72.13	$72.15	$72.10
Purchase #7	$245.44	3.325%	$253.6009	$253.60	$253.60	$253.60
7 purchase totals =	$780.63		$832.9298	$832.93	$832.95	$833.00