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	$33.57	11.615%	$37.4692	$37.47	$37.45	$37.50
Purchase #2	$179.46	6.244%	$190.6655	$190.67	$190.65	$190.70
Purchase #3	$141.78	6.678%	$151.2481	$151.25	$151.25	$151.20
Purchase #4	$55.83	13.296%	$63.2532	$63.25	$63.25	$63.30
Purchase #5	$104.61	4.519%	$109.3373	$109.34	$109.35	$109.30
Purchase #6	$217.66	13.448%	$246.9309	$246.93	$246.95	$246.90
Purchase #7	$47.57	10.794%	$52.7047	$52.70	$52.70	$52.70
7 purchase totals =	$780.48		$851.6089	$851.61	$851.60	$851.60