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	$236.59	5.860%	$250.4542	$250.45	$250.45	$250.50
Purchase #2	$203.42	6.441%	$216.5223	$216.52	$216.50	$216.50
Purchase #3	$113.31	11.618%	$126.4744	$126.47	$126.45	$126.50
Purchase #4	$49.56	11.332%	$55.1761	$55.18	$55.20	$55.20
Purchase #5	$26.95	3.388%	$27.8631	$27.86	$27.85	$27.90
Purchase #6	$207.72	8.112%	$224.5702	$224.57	$224.55	$224.60
Purchase #7	$38.27	6.814%	$40.8777	$40.88	$40.90	$40.90
7 purchase totals =	$875.82		$941.9380	$941.93	$941.90	$942.10