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 $108.55   10.274%   $119.7024   $119.70   $119.70   $119.70  
  Purchase #2 $245.36   11.147%   $272.7103   $272.71   $272.70   $272.70  
  Purchase #3 $90.92   5.253%   $95.696   $95.70   $95.70   $95.70  
  Purchase #4 $156.70   8.775%   $170.4504   $170.45   $170.45   $170.50  
  Purchase #5 $79.83   12.561%   $89.8574   $89.86   $89.85   $89.90  
  Purchase #6 $62.40   7.372%   $67.0001   $67.00   $67.00   $67.00  
  Purchase #7 $24.31   13.344%   $27.5539   $27.55   $27.55   $27.60  
  7 purchase totals = $768.07       $842.9705   $842.97   $842.95   $843.10