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 $69.57   9.794%   $76.3837   $76.38   $76.40   $76.40  
  Purchase #2 $44.72   13.359%   $50.6941   $50.69   $50.70   $50.70  
  Purchase #3 $110.31   6.280%   $117.2375   $117.24   $117.25   $117.20  
  Purchase #4 $142.86   7.285%   $153.2674   $153.27   $153.25   $153.30  
  Purchase #5 $99.50   13.107%   $112.5415   $112.54   $112.55   $112.50  
  Purchase #6 $229.25   8.454%   $248.6308   $248.63   $248.65   $248.60  
  Purchase #7 $61.46   7.475%   $66.0541   $66.05   $66.05   $66.10  
  7 purchase totals = $757.67       $824.8091   $824.80   $824.85   $824.80