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	$189.56	13.591%	$215.3231	$215.32	$215.30	$215.30
Purchase #2	$34.99	13.664%	$39.771	$39.77	$39.75	$39.80
Purchase #3	$86.91	7.105%	$93.085	$93.09	$93.10	$93.10
Purchase #4	$213.52	11.601%	$238.2905	$238.29	$238.30	$238.30
Purchase #5	$52.86	12.750%	$59.5997	$59.60	$59.60	$59.60
Purchase #6	$124.95	12.442%	$140.4963	$140.50	$140.50	$140.50
Purchase #7	$13.26	11.339%	$14.7636	$14.76	$14.75	$14.80
7 purchase totals =	$716.05		$801.3292	$801.33	$801.30	$801.40