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	$33.88	11.750%	$37.8609	$37.86	$37.85	$37.90
Purchase #2	$78.76	11.206%	$87.5858	$87.59	$87.60	$87.60
Purchase #3	$8.43	6.553%	$8.9824	$8.98	$9.00	$9.00
Purchase #4	$6.94	7.761%	$7.4786	$7.48	$7.50	$7.50
Purchase #5	$69.38	3.612%	$71.886	$71.89	$71.90	$71.90
Purchase #6	$48.56	7.384%	$52.1457	$52.15	$52.15	$52.10
Purchase #7	$78.79	6.387%	$83.8223	$83.82	$83.80	$83.80
7 purchase totals =	$324.74		$349.7617	$349.77	$349.80	$349.80