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	$127.52	12.392%	$143.3223	$143.32	$143.30	$143.30
Purchase #2	$65.64	11.738%	$73.3448	$73.34	$73.35	$73.30
Purchase #3	$119.34	8.789%	$129.8288	$129.83	$129.85	$129.80
Purchase #4	$189.39	12.776%	$213.5865	$213.59	$213.60	$213.60
Purchase #5	$119.35	10.703%	$132.124	$132.12	$132.10	$132.10
Purchase #6	$28.46	13.648%	$32.3442	$32.34	$32.35	$32.30
Purchase #7	$134.79	6.502%	$143.554	$143.55	$143.55	$143.60
7 purchase totals =	$784.49		$868.1046	$868.09	$868.10	$868.00