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 $56.54   12.640%   $63.6867   $63.69   $63.70   $63.70  
  Purchase #2 $103.25   4.517%   $107.9138   $107.91   $107.90   $107.90  
  Purchase #3 $174.87   10.846%   $193.8364   $193.84   $193.85   $193.80  
  Purchase #4 $216.54   10.745%   $239.8072   $239.81   $239.80   $239.80  
  Purchase #5 $232.90   10.413%   $257.1519   $257.15   $257.15   $257.20  
  Purchase #6 $125.63   5.273%   $132.2545   $132.25   $132.25   $132.30  
  Purchase #7 $57.60   4.293%   $60.0728   $60.07   $60.05   $60.10  
  7 purchase totals = $967.33       $1,054.7233   $1,054.72   $1,054.70   $1,054.80