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	$133.35	4.682%	$139.5934	$139.59	$139.60	$139.60
Purchase #2	$87.52	8.421%	$94.8901	$94.89	$94.90	$94.90
Purchase #3	$33.88	11.122%	$37.6481	$37.65	$37.65	$37.60
Purchase #4	$14.53	9.513%	$15.9122	$15.91	$15.90	$15.90
Purchase #5	$11.93	5.338%	$12.5668	$12.57	$12.55	$12.60
Purchase #6	$103.94	12.672%	$117.1113	$117.11	$117.10	$117.10
Purchase #7	$33.29	7.641%	$35.8337	$35.83	$35.85	$35.80
7 purchase totals =	$418.44		$453.5556	$453.55	$453.55	$453.50