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	$34.87	11.226%	$38.7845	$38.78	$38.80	$38.80
Purchase #2	$32.65	8.198%	$35.3266	$35.33	$35.35	$35.30
Purchase #3	$37.72	8.405%	$40.8904	$40.89	$40.90	$40.90
Purchase #4	$58.91	7.795%	$63.502	$63.50	$63.50	$63.50
Purchase #5	$208.47	12.489%	$234.5058	$234.51	$234.50	$234.50
Purchase #6	$80.31	12.402%	$90.27	$90.27	$90.25	$90.30
Purchase #7	$62.26	9.374%	$68.0963	$68.10	$68.10	$68.10
7 purchase totals =	$515.19		$571.3756	$571.38	$571.40	$571.40