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	$112.49	13.189%	$127.3263	$127.33	$127.35	$127.30
Purchase #2	$194.51	11.528%	$216.9331	$216.93	$216.95	$216.90
Purchase #3	$140.66	8.377%	$152.4431	$152.44	$152.45	$152.40
Purchase #4	$35.74	12.126%	$40.0738	$40.07	$40.05	$40.10
Purchase #5	$199.69	9.433%	$218.5268	$218.53	$218.55	$218.50
Purchase #6	$72.51	3.655%	$75.1602	$75.16	$75.15	$75.20
Purchase #7	$154.29	8.161%	$166.8816	$166.88	$166.90	$166.90
7 purchase totals =	$909.89		$997.3449	$997.34	$997.40	$997.30