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 $41.48   6.127%   $44.0215   $44.02   $44.00   $44.00  
  Purchase #2 $51.82   5.154%   $54.4908   $54.49   $54.50   $54.50  
  Purchase #3 $190.63   4.213%   $198.6612   $198.66   $198.65   $198.70  
  Purchase #4 $226.32   10.339%   $249.7192   $249.72   $249.70   $249.70  
  Purchase #5 $113.83   9.491%   $124.6336   $124.63   $124.65   $124.60  
  Purchase #6 $29.99   5.358%   $31.5969   $31.60   $31.60   $31.60  
  Purchase #7 $63.96   10.255%   $70.5191   $70.52   $70.50   $70.50  
  7 purchase totals = $718.03       $773.6423   $773.64   $773.60   $773.60