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 $231.26   13.452%   $262.3691   $262.37   $262.35   $262.40  
  Purchase #2 $117.95   6.125%   $125.1744   $125.17   $125.15   $125.20  
  Purchase #3 $55.97   6.357%   $59.528   $59.53   $59.55   $59.50  
  Purchase #4 $83.29   10.535%   $92.0646   $92.06   $92.05   $92.10  
  Purchase #5 $188.29   10.196%   $207.488   $207.49   $207.50   $207.50  
  Purchase #6 $40.95   8.291%   $44.3452   $44.35   $44.35   $44.30  
  Purchase #7 $236.72   13.424%   $268.4973   $268.50   $268.50   $268.50  
  7 purchase totals = $954.43       $1,059.4666   $1,059.47   $1,059.45   $1,059.50