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	$42.46	6.726%	$45.3159	$45.32	$45.30	$45.30
Purchase #2	$110.81	6.134%	$117.6071	$117.61	$117.60	$117.60
Purchase #3	$133.52	13.832%	$151.9885	$151.99	$152.00	$152.00
Purchase #4	$118.83	6.691%	$126.7809	$126.78	$126.80	$126.80
Purchase #5	$73.75	11.838%	$82.4805	$82.48	$82.50	$82.50
Purchase #6	$92.38	9.219%	$100.8965	$100.90	$100.90	$100.90
Purchase #7	$198.97	12.387%	$223.6164	$223.62	$223.60	$223.60
7 purchase totals =	$770.72		$848.6858	$848.70	$848.70	$848.70