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	$217.80	11.306%	$242.4245	$242.42	$242.40	$242.40
Purchase #2	$36.83	5.744%	$38.9455	$38.95	$38.95	$38.90
Purchase #3	$84.33	3.872%	$87.5953	$87.60	$87.60	$87.60
Purchase #4	$26.64	4.297%	$27.7847	$27.78	$27.80	$27.80
Purchase #5	$106.79	4.175%	$111.2485	$111.25	$111.25	$111.20
Purchase #6	$66.73	8.618%	$72.4808	$72.48	$72.50	$72.50
Purchase #7	$69.37	10.125%	$76.3937	$76.39	$76.40	$76.40
7 purchase totals =	$608.49		$656.8730	$656.87	$656.90	$656.80