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	$130.46	10.239%	$143.8178	$143.82	$143.80	$143.80
Purchase #2	$126.76	8.806%	$137.9225	$137.92	$137.90	$137.90
Purchase #3	$133.57	6.859%	$142.7316	$142.73	$142.75	$142.70
Purchase #4	$215.33	12.131%	$241.4517	$241.45	$241.45	$241.50
Purchase #5	$52.67	13.647%	$59.8579	$59.86	$59.85	$59.90
Purchase #6	$83.37	3.378%	$86.1862	$86.19	$86.20	$86.20
Purchase #7	$161.53	11.313%	$179.8039	$179.80	$179.80	$179.80
7 purchase totals =	$903.69		$991.7716	$991.77	$991.75	$991.80