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	$29.47	12.583%	$33.1782	$33.18	$33.20	$33.20
Purchase #2	$40.50	5.752%	$42.8296	$42.83	$42.85	$42.80
Purchase #3	$54.86	13.297%	$62.1547	$62.15	$62.15	$62.20
Purchase #4	$147.66	13.784%	$168.0135	$168.01	$168.00	$168.00
Purchase #5	$136.58	10.707%	$151.2036	$151.20	$151.20	$151.20
Purchase #6	$181.66	6.141%	$192.8157	$192.82	$192.80	$192.80
Purchase #7	$6.42	10.394%	$7.0873	$7.09	$7.10	$7.10
7 purchase totals =	$597.15		$657.2826	$657.28	$657.30	$657.30