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	$29.86	6.792%	$31.8881	$31.89	$31.90	$31.90
Purchase #2	$49.67	6.695%	$52.9954	$53.00	$53.00	$53.00
Purchase #3	$230.37	6.850%	$246.1503	$246.15	$246.15	$246.20
Purchase #4	$167.47	3.125%	$172.7034	$172.70	$172.70	$172.70
Purchase #5	$141.60	6.554%	$150.8805	$150.88	$150.90	$150.90
Purchase #6	$117.73	10.192%	$129.729	$129.73	$129.75	$129.70
Purchase #7	$248.69	10.663%	$275.2078	$275.21	$275.20	$275.20
7 purchase totals =	$985.39		$1,059.5545	$1,059.56	$1,059.60	$1,059.60