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 $236.80   13.675%   $269.1824   $269.18   $269.20   $269.20  
  Purchase #2 $122.90   13.151%   $139.0626   $139.06   $139.05   $139.10  
  Purchase #3 $183.38   4.362%   $191.379   $191.38   $191.40   $191.40  
  Purchase #4 $16.50   8.340%   $17.8761   $17.88   $17.90   $17.90  
  Purchase #5 $225.61   8.817%   $245.502   $245.50   $245.50   $245.50  
  Purchase #6 $135.46   13.308%   $153.487   $153.49   $153.50   $153.50  
  Purchase #7 $241.44   4.505%   $252.3169   $252.32   $252.30   $252.30  
  7 purchase totals = $1,162.09       $1,268.8060   $1,268.81   $1,268.85   $1,268.90