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	$30.57	12.339%	$34.342	$34.34	$34.35	$34.30
Purchase #2	$156.93	11.811%	$175.465	$175.47	$175.45	$175.50
Purchase #3	$119.63	5.494%	$126.2025	$126.20	$126.20	$126.20
Purchase #4	$101.42	10.210%	$111.775	$111.78	$111.80	$111.80
Purchase #5	$63.32	13.408%	$71.8099	$71.81	$71.80	$71.80
Purchase #6	$115.73	13.588%	$131.4554	$131.46	$131.45	$131.50
Purchase #7	$89.78	11.210%	$99.8443	$99.84	$99.85	$99.80
7 purchase totals =	$677.38		$750.8941	$750.90	$750.90	$750.90