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	$38.68	4.769%	$40.5246	$40.52	$40.50	$40.50
Purchase #2	$40.25	6.471%	$42.8546	$42.85	$42.85	$42.90
Purchase #3	$35.61	8.622%	$38.6803	$38.68	$38.70	$38.70
Purchase #4	$30.39	12.368%	$34.1486	$34.15	$34.15	$34.10
Purchase #5	$75.42	3.294%	$77.9043	$77.90	$77.90	$77.90
Purchase #6	$211.65	11.669%	$236.3474	$236.35	$236.35	$236.30
Purchase #7	$78.32	8.799%	$85.2114	$85.21	$85.20	$85.20
7 purchase totals =	$510.32		$555.6712	$555.66	$555.65	$555.60