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	$26.79	5.678%	$28.3111	$28.31	$28.30	$28.30
Purchase #2	$130.48	5.407%	$137.5351	$137.54	$137.55	$137.50
Purchase #3	$198.31	13.364%	$224.8121	$224.81	$224.80	$224.80
Purchase #4	$128.78	13.841%	$146.6044	$146.60	$146.60	$146.60
Purchase #5	$108.64	12.846%	$122.5959	$122.60	$122.60	$122.60
Purchase #6	$244.75	11.363%	$272.5609	$272.56	$272.55	$272.60
Purchase #7	$172.73	10.531%	$190.9202	$190.92	$190.90	$190.90
7 purchase totals =	$1,010.48		$1,123.3397	$1,123.34	$1,123.30	$1,123.30