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	$169.29	13.256%	$191.7311	$191.73	$191.75	$191.70
Purchase #2	$128.34	9.838%	$140.9661	$140.97	$140.95	$141.00
Purchase #3	$34.33	9.159%	$37.4743	$37.47	$37.45	$37.50
Purchase #4	$148.59	7.354%	$159.5173	$159.52	$159.50	$159.50
Purchase #5	$103.74	5.491%	$109.4364	$109.44	$109.45	$109.40
Purchase #6	$146.85	10.400%	$162.1224	$162.12	$162.10	$162.10
Purchase #7	$28.93	4.457%	$30.2194	$30.22	$30.20	$30.20
7 purchase totals =	$760.07		$831.4670	$831.47	$831.40	$831.40