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 $174.32   12.552%   $196.2006   $196.20   $196.20   $196.20  
  Purchase #2 $81.77   13.383%   $92.7133   $92.71   $92.70   $92.70  
  Purchase #3 $232.31   12.420%   $261.1629   $261.16   $261.15   $261.20  
  Purchase #4 $233.61   5.240%   $245.8512   $245.85   $245.85   $245.90  
  Purchase #5 $100.40   6.582%   $107.0083   $107.01   $107.00   $107.00  
  Purchase #6 $169.38   10.297%   $186.8211   $186.82   $186.80   $186.80  
  Purchase #7 $43.33   10.847%   $48.03   $48.03   $48.05   $48.00  
  7 purchase totals = $1,035.12       $1,137.7874   $1,137.78   $1,137.75   $1,137.80