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	$40.26	12.516%	$45.2989	$45.30	$45.30	$45.30
Purchase #2	$161.28	3.777%	$167.3715	$167.37	$167.35	$167.40
Purchase #3	$153.67	5.753%	$162.5106	$162.51	$162.50	$162.50
Purchase #4	$109.83	10.299%	$121.1414	$121.14	$121.15	$121.10
Purchase #5	$245.57	10.384%	$271.07	$271.07	$271.05	$271.10
Purchase #6	$127.49	7.842%	$137.4878	$137.49	$137.50	$137.50
Purchase #7	$77.44	10.118%	$85.2754	$85.28	$85.30	$85.30
7 purchase totals =	$915.54		$990.1556	$990.16	$990.15	$990.20