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	$57.73	3.830%	$59.9411	$59.94	$59.95	$59.90
Purchase #2	$145.82	12.820%	$164.5141	$164.51	$164.50	$164.50
Purchase #3	$89.42	13.350%	$101.3576	$101.36	$101.35	$101.40
Purchase #4	$241.32	13.491%	$273.8765	$273.88	$273.90	$273.90
Purchase #5	$123.67	13.863%	$140.8144	$140.81	$140.80	$140.80
Purchase #6	$196.39	10.324%	$216.6653	$216.67	$216.65	$216.70
Purchase #7	$195.41	13.105%	$221.0185	$221.02	$221.00	$221.00
7 purchase totals =	$1,049.76		$1,178.1875	$1,178.19	$1,178.15	$1,178.20