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 $199.28   13.792%   $226.7647   $226.76   $226.75   $226.80  
  Purchase #2 $41.73   12.413%   $46.9099   $46.91   $46.90   $46.90  
  Purchase #3 $128.80   9.512%   $141.0515   $141.05   $141.05   $141.10  
  Purchase #4 $238.34   9.484%   $260.9442   $260.94   $260.95   $260.90  
  Purchase #5 $230.93   11.279%   $256.9766   $256.98   $257.00   $257.00  
  Purchase #6 $218.36   4.274%   $227.6927   $227.69   $227.70   $227.70  
  Purchase #7 $190.63   3.588%   $197.4698   $197.47   $197.45   $197.50  
  7 purchase totals = $1,248.07       $1,357.8094   $1,357.80   $1,357.80   $1,357.90