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	$32.54	13.439%	$36.9131	$36.91	$36.90	$36.90
Purchase #2	$248.40	8.613%	$269.7947	$269.79	$269.80	$269.80
Purchase #3	$126.56	10.465%	$139.8045	$139.80	$139.80	$139.80
Purchase #4	$60.47	11.745%	$67.5722	$67.57	$67.55	$67.60
Purchase #5	$218.60	10.714%	$242.0208	$242.02	$242.00	$242.00
Purchase #6	$62.53	6.109%	$66.35	$66.35	$66.35	$66.40
Purchase #7	$144.33	3.161%	$148.8923	$148.89	$148.90	$148.90
7 purchase totals =	$893.43		$971.3476	$971.33	$971.30	$971.40