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 $55.44   12.718%   $62.4909   $62.49   $62.50   $62.50  
  Purchase #2 $153.79   7.576%   $165.4411   $165.44   $165.45   $165.40  
  Purchase #3 $142.94   11.716%   $159.6869   $159.69   $159.70   $159.70  
  Purchase #4 $248.31   5.378%   $261.6641   $261.66   $261.65   $261.70  
  Purchase #5 $114.93   9.298%   $125.6162   $125.62   $125.60   $125.60  
  Purchase #6 $200.35   6.745%   $213.8636   $213.86   $213.85   $213.90  
  Purchase #7 $21.37   5.728%   $22.5941   $22.59   $22.60   $22.60  
  7 purchase totals = $937.13       $1,011.3569   $1,011.35   $1,011.35   $1,011.40