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 $216.38   10.131%   $238.3015   $238.30   $238.30   $238.30  
  Purchase #2 $89.72   4.662%   $93.9027   $93.90   $93.90   $93.90  
  Purchase #3 $15.62   11.685%   $17.4452   $17.45   $17.45   $17.40  
  Purchase #4 $137.50   4.555%   $143.7631   $143.76   $143.75   $143.80  
  Purchase #5 $201.31   9.348%   $220.1285   $220.13   $220.15   $220.10  
  Purchase #6 $167.54   12.512%   $188.5026   $188.50   $188.50   $188.50  
  Purchase #7 $123.97   8.193%   $134.1269   $134.13   $134.15   $134.10  
  7 purchase totals = $952.04       $1,036.1705   $1,036.17   $1,036.20   $1,036.10