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 $237.58   10.755%   $263.1317   $263.13   $263.15   $263.10  
  Purchase #2 $192.85   10.709%   $213.5023   $213.50   $213.50   $213.50  
  Purchase #3 $156.55   11.702%   $174.8695   $174.87   $174.85   $174.90  
  Purchase #4 $86.66   9.828%   $95.1769   $95.18   $95.20   $95.20  
  Purchase #5 $59.63   5.167%   $62.7111   $62.71   $62.70   $62.70  
  Purchase #6 $41.25   8.581%   $44.7897   $44.79   $44.80   $44.80  
  Purchase #7 $52.25   7.554%   $56.197   $56.20   $56.20   $56.20  
  7 purchase totals = $826.77       $910.3782   $910.38   $910.40   $910.40