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	$33.99	9.388%	$37.181	$37.18	$37.20	$37.20
Purchase #2	$235.70	11.304%	$262.3435	$262.34	$262.35	$262.30
Purchase #3	$72.59	8.299%	$78.6142	$78.61	$78.60	$78.60
Purchase #4	$230.62	8.637%	$250.5386	$250.54	$250.55	$250.50
Purchase #5	$212.60	10.803%	$235.5672	$235.57	$235.55	$235.60
Purchase #6	$131.85	3.860%	$136.9394	$136.94	$136.95	$136.90
Purchase #7	$73.47	11.139%	$81.6538	$81.65	$81.65	$81.70
7 purchase totals =	$990.82		$1,082.8377	$1,082.83	$1,082.85	$1,082.80