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	$34.47	9.706%	$37.8157	$37.82	$37.80	$37.80
Purchase #2	$100.78	11.569%	$112.4392	$112.44	$112.45	$112.40
Purchase #3	$55.39	11.399%	$61.7039	$61.70	$61.70	$61.70
Purchase #4	$176.97	7.488%	$190.2215	$190.22	$190.20	$190.20
Purchase #5	$142.46	4.220%	$148.4718	$148.47	$148.45	$148.50
Purchase #6	$151.95	10.477%	$167.8698	$167.87	$167.85	$167.90
Purchase #7	$139.92	5.110%	$147.0699	$147.07	$147.05	$147.10
7 purchase totals =	$801.94		$865.5918	$865.59	$865.50	$865.60