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 $37.95   8.435%   $41.1511   $41.15   $41.15   $41.20  
  Purchase #2 $111.42   5.599%   $117.6584   $117.66   $117.65   $117.70  
  Purchase #3 $85.69   3.659%   $88.8254   $88.83   $88.85   $88.80  
  Purchase #4 $146.75   8.159%   $158.7233   $158.72   $158.70   $158.70  
  Purchase #5 $58.62   5.608%   $61.9074   $61.91   $61.90   $61.90  
  Purchase #6 $231.40   11.772%   $258.6404   $258.64   $258.65   $258.60  
  Purchase #7 $48.92   6.531%   $52.115   $52.12   $52.10   $52.10  
  7 purchase totals = $720.75       $779.0210   $779.03   $779.00   $779.00