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	$124.60	11.571%	$139.0175	$139.02	$139.00	$139.00
Purchase #2	$229.25	6.360%	$243.8303	$243.83	$243.85	$243.80
Purchase #3	$78.38	5.707%	$82.8531	$82.85	$82.85	$82.90
Purchase #4	$227.72	5.207%	$239.5774	$239.58	$239.60	$239.60
Purchase #5	$158.95	8.774%	$172.8963	$172.90	$172.90	$172.90
Purchase #6	$84.78	12.393%	$95.2868	$95.29	$95.30	$95.30
Purchase #7	$187.47	6.805%	$200.2273	$200.23	$200.25	$200.20
7 purchase totals =	$1,091.15		$1,173.6887	$1,173.70	$1,173.75	$1,173.70