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 $66.93   8.582%   $72.6739   $72.67   $72.65   $72.70  
  Purchase #2 $24.41   12.833%   $27.5425   $27.54   $27.55   $27.50  
  Purchase #3 $62.65   8.653%   $68.0711   $68.07   $68.05   $68.10  
  Purchase #4 $94.51   3.257%   $97.5882   $97.59   $97.60   $97.60  
  Purchase #5 $221.63   8.854%   $241.2531   $241.25   $241.25   $241.30  
  Purchase #6 $50.55   8.476%   $54.8346   $54.83   $54.85   $54.80  
  Purchase #7 $247.75   7.169%   $265.5112   $265.51   $265.50   $265.50  
  7 purchase totals = $768.43       $827.4746   $827.46   $827.45   $827.50