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 $130.58   13.809%   $148.6118   $148.61   $148.60   $148.60  
  Purchase #2 $227.47   11.870%   $254.4707   $254.47   $254.45   $254.50  
  Purchase #3 $163.39   3.850%   $169.6805   $169.68   $169.70   $169.70  
  Purchase #4 $239.26   6.480%   $254.764   $254.76   $254.75   $254.80  
  Purchase #5 $58.94   8.738%   $64.0902   $64.09   $64.10   $64.10  
  Purchase #6 $242.51   7.359%   $260.3563   $260.36   $260.35   $260.40  
  Purchase #7 $128.66   8.738%   $139.9023   $139.90   $139.90   $139.90  
  7 purchase totals = $1,190.81       $1,291.8758   $1,291.87   $1,291.85   $1,292.00