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	$38.76	4.430%	$40.4771	$40.48	$40.50	$40.50
Purchase #2	$133.92	7.579%	$144.0698	$144.07	$144.05	$144.10
Purchase #3	$223.96	12.472%	$251.8923	$251.89	$251.90	$251.90
Purchase #4	$134.45	12.145%	$150.779	$150.78	$150.80	$150.80
Purchase #5	$14.48	4.222%	$15.0913	$15.09	$15.10	$15.10
Purchase #6	$46.56	11.718%	$52.0159	$52.02	$52.00	$52.00
Purchase #7	$141.30	7.760%	$152.2649	$152.26	$152.25	$152.30
7 purchase totals =	$733.43		$806.5903	$806.59	$806.60	$806.70