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	$136.34	3.656%	$141.3246	$141.32	$141.30	$141.30
Purchase #2	$81.26	8.857%	$88.4572	$88.46	$88.45	$88.50
Purchase #3	$35.68	8.250%	$38.6236	$38.62	$38.60	$38.60
Purchase #4	$241.31	6.342%	$256.6139	$256.61	$256.60	$256.60
Purchase #5	$49.80	4.517%	$52.0495	$52.05	$52.05	$52.00
Purchase #6	$116.30	6.854%	$124.2712	$124.27	$124.25	$124.30
Purchase #7	$175.72	8.485%	$190.6298	$190.63	$190.65	$190.60
7 purchase totals =	$836.41		$891.9698	$891.96	$891.90	$891.90