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	$78.29	6.706%	$83.5401	$83.54	$83.55	$83.50
Purchase #2	$128.48	12.564%	$144.6222	$144.62	$144.60	$144.60
Purchase #3	$209.45	11.677%	$233.9075	$233.91	$233.90	$233.90
Purchase #4	$33.94	9.676%	$37.224	$37.22	$37.20	$37.20
Purchase #5	$34.59	7.180%	$37.0736	$37.07	$37.05	$37.10
Purchase #6	$138.58	7.168%	$148.5134	$148.51	$148.50	$148.50
Purchase #7	$227.26	6.408%	$241.8228	$241.82	$241.80	$241.80
7 purchase totals =	$850.59		$926.7036	$926.69	$926.60	$926.60