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	$234.47	12.279%	$263.2606	$263.26	$263.25	$263.30
Purchase #2	$222.38	7.256%	$238.5159	$238.52	$238.50	$238.50
Purchase #3	$158.30	7.323%	$169.8923	$169.89	$169.90	$169.90
Purchase #4	$178.73	6.280%	$189.9542	$189.95	$189.95	$190.00
Purchase #5	$213.86	8.164%	$231.3195	$231.32	$231.30	$231.30
Purchase #6	$154.33	5.548%	$162.8922	$162.89	$162.90	$162.90
Purchase #7	$26.55	10.388%	$29.308	$29.31	$29.30	$29.30
7 purchase totals =	$1,188.62		$1,285.1427	$1,285.14	$1,285.10	$1,285.20