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	$45.59	9.429%	$49.8887	$49.89	$49.90	$49.90
Purchase #2	$241.87	11.238%	$269.0514	$269.05	$269.05	$269.10
Purchase #3	$50.30	10.276%	$55.4688	$55.47	$55.45	$55.50
Purchase #4	$6.35	10.507%	$7.0172	$7.02	$7.00	$7.00
Purchase #5	$171.29	12.625%	$192.9154	$192.92	$192.90	$192.90
Purchase #6	$55.41	10.808%	$61.3987	$61.40	$61.40	$61.40
Purchase #7	$43.69	3.785%	$45.3437	$45.34	$45.35	$45.30
7 purchase totals =	$614.50		$681.0839	$681.09	$681.05	$681.10