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 $211.61   12.208%   $237.4433   $237.44   $237.45   $237.40  
  Purchase #2 $92.98   12.349%   $104.4621   $104.46   $104.45   $104.50  
  Purchase #3 $146.38   8.335%   $158.5808   $158.58   $158.60   $158.60  
  Purchase #4 $122.39   13.816%   $139.2994   $139.30   $139.30   $139.30  
  Purchase #5 $78.67   10.432%   $86.8769   $86.88   $86.90   $86.90  
  Purchase #6 $123.92   12.766%   $139.7396   $139.74   $139.75   $139.70  
  Purchase #7 $142.59   8.563%   $154.8   $154.80   $154.80   $154.80  
  7 purchase totals = $918.54       $1,021.2021   $1,021.20   $1,021.25   $1,021.20