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	$137.36	13.151%	$155.4242	$155.42	$155.40	$155.40
Purchase #2	$201.39	4.553%	$210.5593	$210.56	$210.55	$210.60
Purchase #3	$215.25	10.512%	$237.8771	$237.88	$237.90	$237.90
Purchase #4	$25.26	13.299%	$28.6193	$28.62	$28.60	$28.60
Purchase #5	$90.56	6.542%	$96.4844	$96.48	$96.50	$96.50
Purchase #6	$244.81	8.344%	$265.2369	$265.24	$265.25	$265.20
Purchase #7	$93.38	7.761%	$100.6272	$100.63	$100.65	$100.60
7 purchase totals =	$1,008.01		$1,094.8284	$1,094.83	$1,094.85	$1,094.80