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 $236.59   12.254%   $265.5817   $265.58   $265.60   $265.60  
  Purchase #2 $206.48   12.554%   $232.4015   $232.40   $232.40   $232.40  
  Purchase #3 $211.39   4.152%   $220.1669   $220.17   $220.15   $220.20  
  Purchase #4 $53.87   7.563%   $57.9442   $57.94   $57.95   $57.90  
  Purchase #5 $89.71   6.164%   $95.2397   $95.24   $95.25   $95.20  
  Purchase #6 $143.73   12.534%   $161.7451   $161.75   $161.75   $161.70  
  Purchase #7 $220.57   8.498%   $239.314   $239.31   $239.30   $239.30  
  7 purchase totals = $1,162.34       $1,272.3931   $1,272.39   $1,272.40   $1,272.30