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	$72.94	8.786%	$79.3485	$79.35	$79.35	$79.30
Purchase #2	$200.42	10.769%	$222.0032	$222.00	$222.00	$222.00
Purchase #3	$117.98	5.511%	$124.4819	$124.48	$124.50	$124.50
Purchase #4	$67.93	5.270%	$71.5099	$71.51	$71.50	$71.50
Purchase #5	$61.58	8.614%	$66.8845	$66.88	$66.90	$66.90
Purchase #6	$186.36	13.142%	$210.8514	$210.85	$210.85	$210.90
Purchase #7	$155.59	8.377%	$168.6238	$168.62	$168.60	$168.60
7 purchase totals =	$862.80		$943.7032	$943.69	$943.70	$943.70