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 $113.31   4.811%   $118.7613   $118.76   $118.75   $118.80  
  Purchase #2 $231.93   11.631%   $258.9058   $258.91   $258.90   $258.90  
  Purchase #3 $52.96   7.488%   $56.9256   $56.93   $56.95   $56.90  
  Purchase #4 $139.80   10.598%   $154.616   $154.62   $154.60   $154.60  
  Purchase #5 $118.86   5.346%   $125.2143   $125.21   $125.20   $125.20  
  Purchase #6 $250.93   13.167%   $283.97   $283.97   $283.95   $284.00  
  Purchase #7 $120.63   13.546%   $136.9705   $136.97   $136.95   $137.00  
  7 purchase totals = $1,028.42       $1,135.3635   $1,135.37   $1,135.30   $1,135.40