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	$78.90	10.477%	$87.1664	$87.17	$87.15	$87.20
Purchase #2	$95.56	4.170%	$99.5449	$99.54	$99.55	$99.50
Purchase #3	$66.32	12.762%	$74.7838	$74.78	$74.80	$74.80
Purchase #4	$40.29	6.207%	$42.7908	$42.79	$42.80	$42.80
Purchase #5	$147.32	6.307%	$156.6115	$156.61	$156.60	$156.60
Purchase #6	$206.73	12.680%	$232.9434	$232.94	$232.95	$232.90
Purchase #7	$46.39	5.331%	$48.8631	$48.86	$48.85	$48.90
7 purchase totals =	$681.51		$742.7039	$742.69	$742.70	$742.70