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 $49.95   5.308%   $52.6013   $52.60   $52.60   $52.60  
  Purchase #2 $228.84   8.193%   $247.5889   $247.59   $247.60   $247.60  
  Purchase #3 $220.47   8.547%   $239.3136   $239.31   $239.30   $239.30  
  Purchase #4 $186.53   12.655%   $210.1354   $210.14   $210.15   $210.10  
  Purchase #5 $241.68   11.177%   $268.6926   $268.69   $268.70   $268.70  
  Purchase #6 $88.73   4.821%   $93.0077   $93.01   $93.00   $93.00  
  Purchase #7 $148.56   8.860%   $161.7224   $161.72   $161.70   $161.70  
  7 purchase totals = $1,164.76       $1,273.0619   $1,273.06   $1,273.05   $1,273.00