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	$30.78	7.652%	$33.1353	$33.14	$33.15	$33.10
Purchase #2	$134.82	5.460%	$142.1812	$142.18	$142.20	$142.20
Purchase #3	$69.47	10.186%	$76.5462	$76.55	$76.55	$76.50
Purchase #4	$63.60	11.817%	$71.1156	$71.12	$71.10	$71.10
Purchase #5	$126.62	3.639%	$131.2277	$131.23	$131.25	$131.20
Purchase #6	$36.97	13.610%	$42.0016	$42.00	$42.00	$42.00
Purchase #7	$216.32	5.219%	$227.6097	$227.61	$227.60	$227.60
7 purchase totals =	$678.58		$723.8173	$723.83	$723.85	$723.70