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 $109.59   7.739%   $118.0712   $118.07   $118.05   $118.10  
  Purchase #2 $70.60   6.514%   $75.1989   $75.20   $75.20   $75.20  
  Purchase #3 $217.55   5.714%   $229.9808   $229.98   $230.00   $230.00  
  Purchase #4 $240.92   12.582%   $271.2326   $271.23   $271.25   $271.20  
  Purchase #5 $99.98   5.602%   $105.5809   $105.58   $105.60   $105.60  
  Purchase #6 $247.27   5.730%   $261.4386   $261.44   $261.45   $261.40  
  Purchase #7 $25.54   3.210%   $26.3598   $26.36   $26.35   $26.40  
  7 purchase totals = $1,011.45       $1,087.8628   $1,087.86   $1,087.90   $1,087.90