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	$18.32	6.561%	$19.522	$19.52	$19.50	$19.50
Purchase #2	$75.81	3.278%	$78.2951	$78.30	$78.30	$78.30
Purchase #3	$91.73	10.636%	$101.4864	$101.49	$101.50	$101.50
Purchase #4	$90.75	11.176%	$100.8922	$100.89	$100.90	$100.90
Purchase #5	$68.51	10.341%	$75.5946	$75.59	$75.60	$75.60
Purchase #6	$68.46	6.265%	$72.749	$72.75	$72.75	$72.70
Purchase #7	$206.79	3.167%	$213.339	$213.34	$213.35	$213.30
7 purchase totals =	$620.37		$661.8783	$661.88	$661.90	$661.80