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	$228.90	7.378%	$245.7882	$245.79	$245.80	$245.80
Purchase #2	$87.83	12.874%	$99.1372	$99.14	$99.15	$99.10
Purchase #3	$136.43	11.657%	$152.3336	$152.33	$152.35	$152.30
Purchase #4	$110.42	10.337%	$121.8341	$121.83	$121.85	$121.80
Purchase #5	$69.86	12.780%	$78.7881	$78.79	$78.80	$78.80
Purchase #6	$54.80	3.704%	$56.8298	$56.83	$56.85	$56.80
Purchase #7	$172.29	10.635%	$190.613	$190.61	$190.60	$190.60
7 purchase totals =	$860.53		$945.3240	$945.32	$945.40	$945.20