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	$27.97	11.245%	$31.1152	$31.12	$31.10	$31.10
Purchase #2	$214.66	5.667%	$226.8248	$226.82	$226.80	$226.80
Purchase #3	$111.57	7.363%	$119.7849	$119.78	$119.80	$119.80
Purchase #4	$187.89	5.119%	$197.5081	$197.51	$197.50	$197.50
Purchase #5	$98.42	10.769%	$109.0188	$109.02	$109.00	$109.00
Purchase #6	$37.47	12.766%	$42.2534	$42.25	$42.25	$42.30
Purchase #7	$185.58	7.566%	$199.621	$199.62	$199.60	$199.60
7 purchase totals =	$863.56		$926.1262	$926.12	$926.05	$926.10