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	$53.81	10.544%	$59.4837	$59.48	$59.50	$59.50
Purchase #2	$217.40	6.502%	$231.5353	$231.54	$231.55	$231.50
Purchase #3	$161.64	6.459%	$172.0803	$172.08	$172.10	$172.10
Purchase #4	$200.39	12.733%	$225.9057	$225.91	$225.90	$225.90
Purchase #5	$44.89	11.260%	$49.9446	$49.94	$49.95	$49.90
Purchase #6	$78.98	5.420%	$83.2607	$83.26	$83.25	$83.30
Purchase #7	$8.62	7.691%	$9.283	$9.28	$9.30	$9.30
7 purchase totals =	$765.73		$831.4933	$831.49	$831.55	$831.50