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	$126.90	7.217%	$136.0584	$136.06	$136.05	$136.10
Purchase #2	$87.31	9.355%	$95.4779	$95.48	$95.50	$95.50
Purchase #3	$46.68	12.442%	$52.4879	$52.49	$52.50	$52.50
Purchase #4	$142.41	8.855%	$155.0204	$155.02	$155.00	$155.00
Purchase #5	$35.77	12.867%	$40.3725	$40.37	$40.35	$40.40
Purchase #6	$34.27	12.260%	$38.4715	$38.47	$38.45	$38.50
Purchase #7	$156.61	6.727%	$167.1452	$167.15	$167.15	$167.10
7 purchase totals =	$629.95		$685.0338	$685.04	$685.00	$685.10