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 $216.97   8.847%   $236.1653   $236.17   $236.15   $236.20  
  Purchase #2 $95.69   11.189%   $106.3968   $106.40   $106.40   $106.40  
  Purchase #3 $79.55   5.802%   $84.1655   $84.17   $84.15   $84.20  
  Purchase #4 $88.74   11.438%   $98.8901   $98.89   $98.90   $98.90  
  Purchase #5 $192.74   3.663%   $199.8001   $199.80   $199.80   $199.80  
  Purchase #6 $16.94   3.695%   $17.5659   $17.57   $17.55   $17.60  
  Purchase #7 $22.58   12.532%   $25.4097   $25.41   $25.40   $25.40  
  7 purchase totals = $713.21       $768.3934   $768.41   $768.35   $768.50