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	$155.38	7.842%	$167.5649	$167.56	$167.55	$167.60
Purchase #2	$140.68	4.306%	$146.7377	$146.74	$146.75	$146.70
Purchase #3	$250.47	9.342%	$273.8689	$273.87	$273.85	$273.90
Purchase #4	$43.51	4.822%	$45.6081	$45.61	$45.60	$45.60
Purchase #5	$73.62	5.635%	$77.7685	$77.77	$77.75	$77.80
Purchase #6	$50.94	8.226%	$55.1303	$55.13	$55.15	$55.10
Purchase #7	$102.39	6.321%	$108.8621	$108.86	$108.85	$108.90
7 purchase totals =	$816.99		$875.5405	$875.54	$875.50	$875.60