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	$133.34	8.128%	$144.1779	$144.18	$144.20	$144.20
Purchase #2	$207.52	8.104%	$224.3374	$224.34	$224.35	$224.30
Purchase #3	$196.54	7.303%	$210.8933	$210.89	$210.90	$210.90
Purchase #4	$172.83	13.654%	$196.4282	$196.43	$196.45	$196.40
Purchase #5	$166.38	13.482%	$188.8114	$188.81	$188.80	$188.80
Purchase #6	$26.28	7.330%	$28.2063	$28.21	$28.20	$28.20
Purchase #7	$34.47	11.475%	$38.4254	$38.43	$38.45	$38.40
7 purchase totals =	$937.36		$1,031.2799	$1,031.29	$1,031.35	$1,031.20