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	$51.52	12.431%	$57.9245	$57.92	$57.90	$57.90
Purchase #2	$180.71	12.547%	$203.3837	$203.38	$203.40	$203.40
Purchase #3	$135.46	4.283%	$141.2618	$141.26	$141.25	$141.30
Purchase #4	$90.96	4.593%	$95.1378	$95.14	$95.15	$95.10
Purchase #5	$224.56	7.826%	$242.1341	$242.13	$242.15	$242.10
Purchase #6	$220.80	4.518%	$230.7757	$230.78	$230.80	$230.80
Purchase #7	$192.42	4.419%	$200.923	$200.92	$200.90	$200.90
7 purchase totals =	$1,096.43		$1,171.5406	$1,171.53	$1,171.55	$1,171.50