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 $139.75   7.678%   $150.48   $150.48   $150.50   $150.50  
  Purchase #2 $44.64   13.544%   $50.686   $50.69   $50.70   $50.70  
  Purchase #3 $180.54   13.360%   $204.6601   $204.66   $204.65   $204.70  
  Purchase #4 $234.28   10.504%   $258.8888   $258.89   $258.90   $258.90  
  Purchase #5 $237.70   3.796%   $246.7231   $246.72   $246.70   $246.70  
  Purchase #6 $123.41   10.333%   $136.162   $136.16   $136.15   $136.20  
  Purchase #7 $19.68   4.509%   $20.5674   $20.57   $20.55   $20.60  
  7 purchase totals = $980.00       $1,068.1674   $1,068.17   $1,068.15   $1,068.30