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	$233.69	6.776%	$249.5248	$249.52	$249.50	$249.50
Purchase #2	$112.73	4.110%	$117.3632	$117.36	$117.35	$117.40
Purchase #3	$36.52	5.261%	$38.4413	$38.44	$38.45	$38.40
Purchase #4	$150.95	12.389%	$169.6512	$169.65	$169.65	$169.70
Purchase #5	$138.38	5.872%	$146.5057	$146.51	$146.50	$146.50
Purchase #6	$244.47	11.107%	$271.6233	$271.62	$271.60	$271.60
Purchase #7	$64.85	9.404%	$70.9485	$70.95	$70.95	$70.90
7 purchase totals =	$981.59		$1,064.0580	$1,064.05	$1,064.00	$1,064.00