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 $108.53   10.197%   $119.5968   $119.60   $119.60   $119.60  
  Purchase #2 $59.25   9.189%   $64.6945   $64.69   $64.70   $64.70  
  Purchase #3 $115.69   9.579%   $126.7719   $126.77   $126.75   $126.80  
  Purchase #4 $14.74   13.250%   $16.6931   $16.69   $16.70   $16.70  
  Purchase #5 $230.86   13.514%   $262.0584   $262.06   $262.05   $262.10  
  Purchase #6 $224.63   10.336%   $247.8478   $247.85   $247.85   $247.80  
  Purchase #7 $173.45   8.679%   $188.5037   $188.50   $188.50   $188.50  
  7 purchase totals = $927.15       $1,026.1662   $1,026.16   $1,026.15   $1,026.20