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	$201.81	9.672%	$221.3291	$221.33	$221.35	$221.30
Purchase #2	$109.89	12.412%	$123.5295	$123.53	$123.55	$123.50
Purchase #3	$20.27	9.799%	$22.2563	$22.26	$22.25	$22.30
Purchase #4	$33.34	6.330%	$35.4504	$35.45	$35.45	$35.50
Purchase #5	$11.74	3.324%	$12.1302	$12.13	$12.15	$12.10
Purchase #6	$176.54	6.233%	$187.5437	$187.54	$187.55	$187.50
Purchase #7	$26.25	13.755%	$29.8607	$29.86	$29.85	$29.90
7 purchase totals =	$579.84		$632.0999	$632.10	$632.15	$632.10