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 $117.79   12.707%   $132.7576   $132.76   $132.75   $132.80  
  Purchase #2 $211.70   6.572%   $225.6129   $225.61   $225.60   $225.60  
  Purchase #3 $76.91   5.505%   $81.1439   $81.14   $81.15   $81.10  
  Purchase #4 $58.85   12.811%   $66.3893   $66.39   $66.40   $66.40  
  Purchase #5 $193.77   13.673%   $220.2642   $220.26   $220.25   $220.30  
  Purchase #6 $243.87   13.597%   $277.029   $277.03   $277.05   $277.00  
  Purchase #7 $32.73   13.187%   $37.0461   $37.05   $37.05   $37.00  
  7 purchase totals = $935.62       $1,040.2430   $1,040.24   $1,040.25   $1,040.20