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 $54.92   8.402%   $59.5344   $59.53   $59.55   $59.50  
  Purchase #2 $234.84   11.466%   $261.7668   $261.77   $261.75   $261.80  
  Purchase #3 $146.55   8.558%   $159.0917   $159.09   $159.10   $159.10  
  Purchase #4 $167.67   8.800%   $182.425   $182.43   $182.45   $182.40  
  Purchase #5 $67.64   10.247%   $74.5711   $74.57   $74.55   $74.60  
  Purchase #6 $161.98   8.398%   $175.5831   $175.58   $175.60   $175.60  
  Purchase #7 $10.33   5.192%   $10.8663   $10.87   $10.85   $10.90  
  7 purchase totals = $843.93       $923.8384   $923.84   $923.85   $923.90