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	$6.25	5.520%	$6.595	$6.60	$6.60	$6.60
Purchase #2	$105.62	4.669%	$110.5514	$110.55	$110.55	$110.60
Purchase #3	$80.37	4.219%	$83.7608	$83.76	$83.75	$83.80
Purchase #4	$35.80	11.863%	$40.047	$40.05	$40.05	$40.00
Purchase #5	$94.30	5.620%	$99.5997	$99.60	$99.60	$99.60
Purchase #6	$211.49	5.478%	$223.0754	$223.08	$223.10	$223.10
Purchase #7	$117.30	11.797%	$131.1379	$131.14	$131.15	$131.10
7 purchase totals =	$651.13		$694.7672	$694.78	$694.80	$694.80