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	$249.32	9.735%	$273.5913	$273.59	$273.60	$273.60
Purchase #2	$140.51	11.406%	$156.5366	$156.54	$156.55	$156.50
Purchase #3	$57.45	10.620%	$63.5512	$63.55	$63.55	$63.60
Purchase #4	$84.57	7.476%	$90.8925	$90.89	$90.90	$90.90
Purchase #5	$92.36	3.331%	$95.4365	$95.44	$95.45	$95.40
Purchase #6	$195.64	8.321%	$211.9192	$211.92	$211.90	$211.90
Purchase #7	$63.81	9.470%	$69.8528	$69.85	$69.85	$69.90
7 purchase totals =	$883.66		$961.7801	$961.78	$961.80	$961.80