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 $119.53   4.316%   $124.6889   $124.69   $124.70   $124.70  
  Purchase #2 $49.25   9.358%   $53.8588   $53.86   $53.85   $53.90  
  Purchase #3 $104.87   10.296%   $115.6674   $115.67   $115.65   $115.70  
  Purchase #4 $178.77   10.732%   $197.9556   $197.96   $197.95   $198.00  
  Purchase #5 $165.28   3.256%   $170.6615   $170.66   $170.65   $170.70  
  Purchase #6 $146.33   3.669%   $151.6988   $151.70   $151.70   $151.70  
  Purchase #7 $74.51   5.758%   $78.8003   $78.80   $78.80   $78.80  
  7 purchase totals = $838.54       $893.3313   $893.34   $893.30   $893.50