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 $46.73   4.129%   $48.6595   $48.66   $48.65   $48.70  
  Purchase #2 $135.72   4.195%   $141.4135   $141.41   $141.40   $141.40  
  Purchase #3 $106.69   6.577%   $113.707   $113.71   $113.70   $113.70  
  Purchase #4 $229.98   9.841%   $252.6123   $252.61   $252.60   $252.60  
  Purchase #5 $32.63   10.802%   $36.1547   $36.15   $36.15   $36.20  
  Purchase #6 $29.55   6.565%   $31.49   $31.49   $31.50   $31.50  
  Purchase #7 $77.87   7.767%   $83.9182   $83.92   $83.90   $83.90  
  7 purchase totals = $659.17       $707.9552   $707.95   $707.90   $708.00