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	$37.57	12.376%	$42.2197	$42.22	$42.20	$42.20
Purchase #2	$145.78	13.791%	$165.8845	$165.88	$165.90	$165.90
Purchase #3	$172.65	7.827%	$186.1633	$186.16	$186.15	$186.20
Purchase #4	$102.49	9.129%	$111.8463	$111.85	$111.85	$111.80
Purchase #5	$117.30	4.807%	$122.9386	$122.94	$122.95	$122.90
Purchase #6	$81.48	5.108%	$85.642	$85.64	$85.65	$85.60
Purchase #7	$238.56	12.306%	$267.9172	$267.92	$267.90	$267.90
7 purchase totals =	$895.83		$982.6116	$982.61	$982.60	$982.50