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	$47.69	3.691%	$49.4502	$49.45	$49.45	$49.50
Purchase #2	$33.47	5.290%	$35.2406	$35.24	$35.25	$35.20
Purchase #3	$153.92	12.442%	$173.0707	$173.07	$173.05	$173.10
Purchase #4	$77.87	5.623%	$82.2486	$82.25	$82.25	$82.20
Purchase #5	$124.89	5.242%	$131.4367	$131.44	$131.45	$131.40
Purchase #6	$218.78	11.168%	$243.2134	$243.21	$243.20	$243.20
Purchase #7	$143.65	8.506%	$155.8689	$155.87	$155.85	$155.90
7 purchase totals =	$800.27		$870.5291	$870.53	$870.50	$870.50