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 $226.34   10.521%   $250.1532   $250.15   $250.15   $250.20  
  Purchase #2 $245.29   4.347%   $255.9528   $255.95   $255.95   $256.00  
  Purchase #3 $17.33   10.235%   $19.1037   $19.10   $19.10   $19.10  
  Purchase #4 $67.48   5.369%   $71.103   $71.10   $71.10   $71.10  
  Purchase #5 $191.68   10.723%   $212.2338   $212.23   $212.25   $212.20  
  Purchase #6 $102.91   6.256%   $109.348   $109.35   $109.35   $109.30  
  Purchase #7 $188.73   3.443%   $195.228   $195.23   $195.25   $195.20  
  7 purchase totals = $1,039.76       $1,113.1225   $1,113.11   $1,113.15   $1,113.10