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	$51.69	11.497%	$57.6328	$57.63	$57.65	$57.60
Purchase #2	$45.50	10.598%	$50.3221	$50.32	$50.30	$50.30
Purchase #3	$71.31	7.810%	$76.8793	$76.88	$76.90	$76.90
Purchase #4	$170.60	11.740%	$190.6284	$190.63	$190.65	$190.60
Purchase #5	$224.79	8.420%	$243.7173	$243.72	$243.70	$243.70
Purchase #6	$71.71	4.506%	$74.9413	$74.94	$74.95	$74.90
Purchase #7	$65.75	10.602%	$72.7208	$72.72	$72.70	$72.70
7 purchase totals =	$701.35		$766.8420	$766.84	$766.85	$766.70