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 $226.83   7.653%   $244.1893   $244.19   $244.20   $244.20  
  Purchase #2 $16.54   13.704%   $18.8066   $18.81   $18.80   $18.80  
  Purchase #3 $218.99   6.265%   $232.7097   $232.71   $232.70   $232.70  
  Purchase #4 $247.34   8.675%   $268.7967   $268.80   $268.80   $268.80  
  Purchase #5 $122.51   13.874%   $139.507   $139.51   $139.50   $139.50  
  Purchase #6 $96.45   6.506%   $102.725   $102.73   $102.75   $102.70  
  Purchase #7 $52.40   12.318%   $58.8546   $58.85   $58.85   $58.90  
  7 purchase totals = $981.06       $1,065.5889   $1,065.60   $1,065.60   $1,065.60