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	$218.46	11.188%	$242.9013	$242.90	$242.90	$242.90
Purchase #2	$55.56	12.197%	$62.3367	$62.34	$62.35	$62.30
Purchase #3	$37.47	6.864%	$40.0419	$40.04	$40.05	$40.00
Purchase #4	$55.53	13.265%	$62.8961	$62.90	$62.90	$62.90
Purchase #5	$24.83	5.584%	$26.2165	$26.22	$26.20	$26.20
Purchase #6	$55.62	7.361%	$59.7142	$59.71	$59.70	$59.70
Purchase #7	$129.80	10.349%	$143.233	$143.23	$143.25	$143.20
7 purchase totals =	$577.27		$637.3397	$637.34	$637.35	$637.20