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	$84.82	5.327%	$89.3384	$89.34	$89.35	$89.30
Purchase #2	$33.97	3.728%	$35.2364	$35.24	$35.25	$35.20
Purchase #3	$30.41	10.194%	$33.51	$33.51	$33.50	$33.50
Purchase #4	$46.77	8.711%	$50.8441	$50.84	$50.85	$50.80
Purchase #5	$230.38	8.548%	$250.0729	$250.07	$250.05	$250.10
Purchase #6	$46.98	4.529%	$49.1077	$49.11	$49.10	$49.10
Purchase #7	$88.82	13.869%	$101.1384	$101.14	$101.15	$101.10
7 purchase totals =	$562.15		$609.2479	$609.25	$609.25	$609.10