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 $71.92   13.643%   $81.732   $81.73   $81.75   $81.70  
  Purchase #2 $246.28   6.336%   $261.8843   $261.88   $261.90   $261.90  
  Purchase #3 $9.67   10.233%   $10.6595   $10.66   $10.65   $10.70  
  Purchase #4 $82.73   3.669%   $85.7654   $85.77   $85.75   $85.80  
  Purchase #5 $113.35   10.625%   $125.3934   $125.39   $125.40   $125.40  
  Purchase #6 $243.90   5.197%   $256.5755   $256.58   $256.60   $256.60  
  Purchase #7 $19.78   5.434%   $20.8548   $20.85   $20.85   $20.90  
  7 purchase totals = $787.63       $842.8649   $842.86   $842.90   $843.00