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	$42.78	8.368%	$46.3598	$46.36	$46.35	$46.40
Purchase #2	$84.94	3.655%	$88.0446	$88.04	$88.05	$88.00
Purchase #3	$239.60	8.451%	$259.8486	$259.85	$259.85	$259.80
Purchase #4	$51.47	6.568%	$54.8505	$54.85	$54.85	$54.90
Purchase #5	$81.90	6.765%	$87.4405	$87.44	$87.45	$87.40
Purchase #6	$212.47	3.314%	$219.5113	$219.51	$219.50	$219.50
Purchase #7	$36.59	10.790%	$40.5381	$40.54	$40.55	$40.50
7 purchase totals =	$749.75		$796.5934	$796.59	$796.60	$796.50