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	$133.52	12.441%	$150.1312	$150.13	$150.15	$150.10
Purchase #2	$218.39	9.406%	$238.9318	$238.93	$238.95	$238.90
Purchase #3	$146.99	13.678%	$167.0953	$167.10	$167.10	$167.10
Purchase #4	$60.29	11.697%	$67.3421	$67.34	$67.35	$67.30
Purchase #5	$176.78	4.531%	$184.7899	$184.79	$184.80	$184.80
Purchase #6	$140.98	7.563%	$151.6423	$151.64	$151.65	$151.60
Purchase #7	$12.27	7.219%	$13.1558	$13.16	$13.15	$13.20
7 purchase totals =	$889.22		$973.0884	$973.09	$973.15	$973.00