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	$7.59	3.590%	$7.8625	$7.86	$7.85	$7.90
Purchase #2	$125.86	11.139%	$139.8795	$139.88	$139.90	$139.90
Purchase #3	$190.88	13.182%	$216.0418	$216.04	$216.05	$216.00
Purchase #4	$187.91	13.366%	$213.0261	$213.03	$213.05	$213.00
Purchase #5	$172.93	9.255%	$188.9347	$188.93	$188.95	$188.90
Purchase #6	$109.34	7.556%	$117.6017	$117.60	$117.60	$117.60
Purchase #7	$244.38	5.803%	$258.5614	$258.56	$258.55	$258.60
7 purchase totals =	$1,038.89		$1,141.9077	$1,141.90	$1,141.95	$1,141.90