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	$11.48	12.347%	$12.8974	$12.90	$12.90	$12.90
Purchase #2	$49.35	11.772%	$55.1595	$55.16	$55.15	$55.20
Purchase #3	$230.30	3.677%	$238.7681	$238.77	$238.75	$238.80
Purchase #4	$96.42	5.269%	$101.5004	$101.50	$101.50	$101.50
Purchase #5	$39.29	3.716%	$40.75	$40.75	$40.75	$40.80
Purchase #6	$42.58	7.814%	$45.9072	$45.91	$45.90	$45.90
Purchase #7	$206.45	4.648%	$216.0458	$216.05	$216.05	$216.00
7 purchase totals =	$675.87		$711.0284	$711.04	$711.00	$711.10