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	$205.47	8.490%	$222.9144	$222.91	$222.90	$222.90
Purchase #2	$21.86	10.406%	$24.1348	$24.13	$24.15	$24.10
Purchase #3	$116.53	12.433%	$131.0182	$131.02	$131.00	$131.00
Purchase #4	$222.31	11.385%	$247.62	$247.62	$247.60	$247.60
Purchase #5	$18.35	9.373%	$20.0699	$20.07	$20.05	$20.10
Purchase #6	$205.44	5.554%	$216.8501	$216.85	$216.85	$216.90
Purchase #7	$49.56	10.621%	$54.8238	$54.82	$54.80	$54.80
7 purchase totals =	$839.52		$917.4312	$917.42	$917.35	$917.40