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 $119.80   12.659%   $134.9655   $134.97   $134.95   $135.00  
  Purchase #2 $70.56   3.585%   $73.0896   $73.09   $73.10   $73.10  
  Purchase #3 $229.59   5.667%   $242.6009   $242.60   $242.60   $242.60  
  Purchase #4 $136.78   3.737%   $141.8915   $141.89   $141.90   $141.90  
  Purchase #5 $14.85   4.184%   $15.4713   $15.47   $15.45   $15.50  
  Purchase #6 $13.91   5.596%   $14.6884   $14.69   $14.70   $14.70  
  Purchase #7 $241.82   7.135%   $259.0739   $259.07   $259.05   $259.10  
  7 purchase totals = $827.31       $881.7811   $881.78   $881.75   $881.90