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	$90.54	10.816%	$100.3328	$100.33	$100.35	$100.30
Purchase #2	$46.61	10.698%	$51.5963	$51.60	$51.60	$51.60
Purchase #3	$204.26	11.609%	$227.9725	$227.97	$227.95	$228.00
Purchase #4	$198.85	7.182%	$213.1314	$213.13	$213.15	$213.10
Purchase #5	$128.78	8.320%	$139.4945	$139.49	$139.50	$139.50
Purchase #6	$203.34	8.393%	$220.4063	$220.41	$220.40	$220.40
Purchase #7	$130.72	7.490%	$140.5109	$140.51	$140.50	$140.50
7 purchase totals =	$1,003.10		$1,093.4447	$1,093.44	$1,093.45	$1,093.40