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 $92.69   6.415%   $98.6361   $98.64   $98.65   $98.60  
  Purchase #2 $112.70   5.730%   $119.1577   $119.16   $119.15   $119.20  
  Purchase #3 $239.92   4.569%   $250.8819   $250.88   $250.90   $250.90  
  Purchase #4 $154.94   9.815%   $170.1474   $170.15   $170.15   $170.10  
  Purchase #5 $53.97   12.758%   $60.8555   $60.86   $60.85   $60.90  
  Purchase #6 $125.83   11.816%   $140.6981   $140.70   $140.70   $140.70  
  Purchase #7 $99.70   6.170%   $105.8515   $105.85   $105.85   $105.90  
  7 purchase totals = $879.75       $946.2282   $946.24   $946.25   $946.30