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	$37.31	11.123%	$41.46	$41.46	$41.45	$41.50
Purchase #2	$67.51	5.817%	$71.4371	$71.44	$71.45	$71.40
Purchase #3	$133.69	5.151%	$140.5764	$140.58	$140.60	$140.60
Purchase #4	$37.93	7.225%	$40.6704	$40.67	$40.65	$40.70
Purchase #5	$189.51	7.395%	$203.5243	$203.52	$203.50	$203.50
Purchase #6	$35.68	10.793%	$39.5309	$39.53	$39.55	$39.50
Purchase #7	$142.31	5.705%	$150.4288	$150.43	$150.45	$150.40
7 purchase totals =	$643.94		$687.6279	$687.63	$687.65	$687.60