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	$52.55	12.742%	$59.2459	$59.25	$59.25	$59.20
Purchase #2	$25.47	8.155%	$27.5471	$27.55	$27.55	$27.50
Purchase #3	$133.37	13.155%	$150.9148	$150.91	$150.90	$150.90
Purchase #4	$165.99	3.600%	$171.9656	$171.97	$171.95	$172.00
Purchase #5	$81.92	6.406%	$87.1678	$87.17	$87.15	$87.20
Purchase #6	$199.38	4.746%	$208.8426	$208.84	$208.85	$208.80
Purchase #7	$52.80	3.813%	$54.8133	$54.81	$54.80	$54.80
7 purchase totals =	$711.48		$760.4971	$760.50	$760.45	$760.40