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	$123.90	4.777%	$129.8187	$129.82	$129.80	$129.80
Purchase #2	$40.55	12.241%	$45.5137	$45.51	$45.50	$45.50
Purchase #3	$48.42	12.487%	$54.4662	$54.47	$54.45	$54.50
Purchase #4	$68.26	4.777%	$71.5208	$71.52	$71.50	$71.50
Purchase #5	$153.91	11.438%	$171.5142	$171.51	$171.50	$171.50
Purchase #6	$227.57	12.584%	$256.2074	$256.21	$256.20	$256.20
Purchase #7	$164.57	4.804%	$172.4759	$172.48	$172.50	$172.50
7 purchase totals =	$827.18		$901.5169	$901.52	$901.45	$901.50