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 $38.71   12.518%   $43.5557   $43.56   $43.55   $43.60  
  Purchase #2 $118.29   3.665%   $122.6253   $122.63   $122.65   $122.60  
  Purchase #3 $53.89   3.177%   $55.6021   $55.60   $55.60   $55.60  
  Purchase #4 $211.69   9.397%   $231.5825   $231.58   $231.60   $231.60  
  Purchase #5 $244.58   8.440%   $265.2226   $265.22   $265.20   $265.20  
  Purchase #6 $162.84   8.790%   $177.1536   $177.15   $177.15   $177.20  
  Purchase #7 $51.26   8.357%   $55.5438   $55.54   $55.55   $55.50  
  7 purchase totals = $881.26       $951.2856   $951.28   $951.30   $951.30