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	$16.94	7.213%	$18.1619	$18.16	$18.15	$18.20
Purchase #2	$64.40	10.677%	$71.276	$71.28	$71.30	$71.30
Purchase #3	$236.98	7.803%	$255.4715	$255.47	$255.45	$255.50
Purchase #4	$231.41	12.384%	$260.0678	$260.07	$260.05	$260.10
Purchase #5	$33.43	3.715%	$34.6719	$34.67	$34.65	$34.70
Purchase #6	$57.78	6.492%	$61.5311	$61.53	$61.55	$61.50
Purchase #7	$98.44	5.209%	$103.5677	$103.57	$103.55	$103.60
7 purchase totals =	$739.38		$804.7479	$804.75	$804.70	$804.90