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 $212.63   6.816%   $227.1229   $227.12   $227.10   $227.10  
  Purchase #2 $121.67   4.270%   $126.8653   $126.87   $126.85   $126.90  
  Purchase #3 $246.69   6.502%   $262.7298   $262.73   $262.75   $262.70  
  Purchase #4 $66.29   8.125%   $71.6761   $71.68   $71.70   $71.70  
  Purchase #5 $200.80   5.645%   $212.1352   $212.14   $212.15   $212.10  
  Purchase #6 $224.70   7.728%   $242.0648   $242.06   $242.05   $242.10  
  Purchase #7 $108.81   3.669%   $112.8022   $112.80   $112.80   $112.80  
  7 purchase totals = $1,181.59       $1,255.3963   $1,255.40   $1,255.40   $1,255.40