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	$67.83	5.720%	$71.7099	$71.71	$71.70	$71.70
Purchase #2	$246.63	11.353%	$274.6299	$274.63	$274.65	$274.60
Purchase #3	$46.36	10.164%	$51.072	$51.07	$51.05	$51.10
Purchase #4	$38.38	11.787%	$42.9039	$42.90	$42.90	$42.90
Purchase #5	$72.48	5.476%	$76.449	$76.45	$76.45	$76.40
Purchase #6	$98.40	11.799%	$110.0102	$110.01	$110.00	$110.00
Purchase #7	$78.94	8.430%	$85.5946	$85.59	$85.60	$85.60
7 purchase totals =	$649.02		$712.3695	$712.36	$712.35	$712.30