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	$86.47	12.633%	$97.3938	$97.39	$97.40	$97.40
Purchase #2	$124.40	11.136%	$138.2532	$138.25	$138.25	$138.30
Purchase #3	$77.43	10.756%	$85.7584	$85.76	$85.75	$85.80
Purchase #4	$113.93	4.676%	$119.2574	$119.26	$119.25	$119.30
Purchase #5	$139.81	13.677%	$158.9318	$158.93	$158.95	$158.90
Purchase #6	$162.69	6.156%	$172.7052	$172.71	$172.70	$172.70
Purchase #7	$6.60	13.392%	$7.4839	$7.48	$7.50	$7.50
7 purchase totals =	$711.33		$779.7837	$779.78	$779.80	$779.90