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	$124.39	9.336%	$136.0031	$136.00	$136.00	$136.00
Purchase #2	$203.41	13.733%	$231.3443	$231.34	$231.35	$231.30
Purchase #3	$22.77	7.649%	$24.5117	$24.51	$24.50	$24.50
Purchase #4	$89.50	13.517%	$101.5977	$101.60	$101.60	$101.60
Purchase #5	$37.68	7.424%	$40.4774	$40.48	$40.50	$40.50
Purchase #6	$139.67	4.603%	$146.099	$146.10	$146.10	$146.10
Purchase #7	$98.81	7.609%	$106.3285	$106.33	$106.35	$106.30
7 purchase totals =	$716.23		$786.3617	$786.36	$786.40	$786.30