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 $228.97   12.387%   $257.3325   $257.33   $257.35   $257.30  
  Purchase #2 $214.92   9.768%   $235.9134   $235.91   $235.90   $235.90  
  Purchase #3 $181.89   7.417%   $195.3808   $195.38   $195.40   $195.40  
  Purchase #4 $178.25   11.242%   $198.2889   $198.29   $198.30   $198.30  
  Purchase #5 $204.81   13.565%   $232.5925   $232.59   $232.60   $232.60  
  Purchase #6 $234.70   3.833%   $243.6961   $243.70   $243.70   $243.70  
  Purchase #7 $230.80   13.177%   $261.2125   $261.21   $261.20   $261.20  
  7 purchase totals = $1,474.34       $1,624.4167   $1,624.41   $1,624.45   $1,624.40