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	$140.77	6.806%	$150.3508	$150.35	$150.35	$150.40
Purchase #2	$34.53	12.550%	$38.8635	$38.86	$38.85	$38.90
Purchase #3	$121.54	7.798%	$131.0177	$131.02	$131.00	$131.00
Purchase #4	$73.68	3.802%	$76.4813	$76.48	$76.50	$76.50
Purchase #5	$63.56	12.504%	$71.5075	$71.51	$71.50	$71.50
Purchase #6	$45.43	7.867%	$49.004	$49.00	$49.00	$49.00
Purchase #7	$87.38	9.440%	$95.6287	$95.63	$95.65	$95.60
7 purchase totals =	$566.89		$612.8535	$612.85	$612.85	$612.90