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 $126.37   5.806%   $133.707   $133.71   $133.70   $133.70  
  Purchase #2 $40.42   8.270%   $43.7627   $43.76   $43.75   $43.80  
  Purchase #3 $69.53   11.698%   $77.6636   $77.66   $77.65   $77.70  
  Purchase #4 $117.89   6.341%   $125.3654   $125.37   $125.35   $125.40  
  Purchase #5 $22.59   6.173%   $23.9845   $23.98   $24.00   $24.00  
  Purchase #6 $95.53   12.402%   $107.3776   $107.38   $107.40   $107.40  
  Purchase #7 $235.49   6.745%   $251.3738   $251.37   $251.35   $251.40  
  7 purchase totals = $707.82       $763.2346   $763.23   $763.20   $763.40