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	$61.39	6.432%	$65.3386	$65.34	$65.35	$65.30
Purchase #2	$127.98	7.631%	$137.7462	$137.75	$137.75	$137.70
Purchase #3	$66.89	6.409%	$71.177	$71.18	$71.20	$71.20
Purchase #4	$100.55	12.238%	$112.8553	$112.86	$112.85	$112.90
Purchase #5	$89.82	12.737%	$101.2604	$101.26	$101.25	$101.30
Purchase #6	$123.91	11.413%	$138.0518	$138.05	$138.05	$138.10
Purchase #7	$36.39	6.281%	$38.6757	$38.68	$38.70	$38.70
7 purchase totals =	$606.93		$665.1050	$665.12	$665.15	$665.20