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	$152.98	12.355%	$171.8807	$171.88	$171.90	$171.90
Purchase #2	$60.95	7.160%	$65.314	$65.31	$65.30	$65.30
Purchase #3	$246.47	7.536%	$265.044	$265.04	$265.05	$265.00
Purchase #4	$149.59	8.660%	$162.5445	$162.54	$162.55	$162.50
Purchase #5	$229.52	10.442%	$253.4865	$253.49	$253.50	$253.50
Purchase #6	$164.82	12.610%	$185.6038	$185.60	$185.60	$185.60
Purchase #7	$205.38	4.102%	$213.8047	$213.80	$213.80	$213.80
7 purchase totals =	$1,209.71		$1,317.6782	$1,317.66	$1,317.70	$1,317.60