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 $127.58   8.215%   $138.0607   $138.06   $138.05   $138.10  
  Purchase #2 $220.91   5.610%   $233.3031   $233.30   $233.30   $233.30  
  Purchase #3 $139.50   7.139%   $149.4589   $149.46   $149.45   $149.50  
  Purchase #4 $56.43   10.856%   $62.556   $62.56   $62.55   $62.60  
  Purchase #5 $193.92   10.801%   $214.8653   $214.87   $214.85   $214.90  
  Purchase #6 $250.57   5.246%   $263.7149   $263.71   $263.70   $263.70  
  Purchase #7 $205.68   9.410%   $225.0345   $225.03   $225.05   $225.00  
  7 purchase totals = $1,194.59       $1,286.9934   $1,286.99   $1,286.95   $1,287.10