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 $188.59   4.767%   $197.5801   $197.58   $197.60   $197.60  
  Purchase #2 $235.37   8.161%   $254.5785   $254.58   $254.60   $254.60  
  Purchase #3 $122.82   8.236%   $132.9355   $132.94   $132.95   $132.90  
  Purchase #4 $187.64   7.366%   $201.4616   $201.46   $201.45   $201.50  
  Purchase #5 $94.29   11.261%   $104.908   $104.91   $104.90   $104.90  
  Purchase #6 $76.73   6.649%   $81.8318   $81.83   $81.85   $81.80  
  Purchase #7 $26.87   4.659%   $28.1219   $28.12   $28.10   $28.10  
  7 purchase totals = $932.31       $1,001.4174   $1,001.42   $1,001.45   $1,001.40