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	$15.33	9.258%	$16.7493	$16.75	$16.75	$16.70
Purchase #2	$125.76	8.847%	$136.886	$136.89	$136.90	$136.90
Purchase #3	$86.28	3.840%	$89.5932	$89.59	$89.60	$89.60
Purchase #4	$13.32	4.443%	$13.9118	$13.91	$13.90	$13.90
Purchase #5	$216.84	10.210%	$238.9794	$238.98	$239.00	$239.00
Purchase #6	$157.37	3.496%	$162.8717	$162.87	$162.85	$162.90
Purchase #7	$195.90	8.143%	$211.8521	$211.85	$211.85	$211.90
7 purchase totals =	$810.80		$870.8435	$870.84	$870.85	$870.90