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	$43.94	13.667%	$49.9453	$49.95	$49.95	$49.90
Purchase #2	$142.74	6.448%	$151.9439	$151.94	$151.95	$151.90
Purchase #3	$74.87	4.499%	$78.2384	$78.24	$78.25	$78.20
Purchase #4	$226.47	7.659%	$243.8153	$243.82	$243.80	$243.80
Purchase #5	$201.51	3.449%	$208.4601	$208.46	$208.45	$208.50
Purchase #6	$58.73	5.443%	$61.9267	$61.93	$61.95	$61.90
Purchase #7	$34.45	8.313%	$37.3138	$37.31	$37.30	$37.30
7 purchase totals =	$782.71		$831.6435	$831.65	$831.65	$831.50