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 $91.99   4.198%   $95.8517   $95.85   $95.85   $95.90  
  Purchase #2 $90.44   4.709%   $94.6988   $94.70   $94.70   $94.70  
  Purchase #3 $161.44   5.806%   $170.8132   $170.81   $170.80   $170.80  
  Purchase #4 $224.72   9.455%   $245.9673   $245.97   $245.95   $246.00  
  Purchase #5 $45.72   10.174%   $50.3716   $50.37   $50.35   $50.40  
  Purchase #6 $248.55   4.439%   $259.5831   $259.58   $259.60   $259.60  
  Purchase #7 $168.64   10.540%   $186.4147   $186.41   $186.40   $186.40  
  7 purchase totals = $1,031.50       $1,103.7004   $1,103.69   $1,103.65   $1,103.80