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	$140.97	10.187%	$155.3306	$155.33	$155.35	$155.30
Purchase #2	$33.38	6.709%	$35.6195	$35.62	$35.60	$35.60
Purchase #3	$191.51	3.614%	$198.4312	$198.43	$198.45	$198.40
Purchase #4	$79.85	5.764%	$84.4526	$84.45	$84.45	$84.50
Purchase #5	$133.38	6.158%	$141.5935	$141.59	$141.60	$141.60
Purchase #6	$13.92	13.730%	$15.8312	$15.83	$15.85	$15.80
Purchase #7	$43.91	3.611%	$45.4956	$45.50	$45.50	$45.50
7 purchase totals =	$636.92		$676.7542	$676.75	$676.80	$676.70