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 $242.95   8.873%   $264.507   $264.51   $264.50   $264.50  
  Purchase #2 $202.44   13.130%   $229.0204   $229.02   $229.00   $229.00  
  Purchase #3 $199.73   10.668%   $221.0372   $221.04   $221.05   $221.00  
  Purchase #4 $98.83   6.193%   $104.9505   $104.95   $104.95   $105.00  
  Purchase #5 $179.32   12.237%   $201.2634   $201.26   $201.25   $201.30  
  Purchase #6 $24.30   7.797%   $26.1947   $26.19   $26.20   $26.20  
  Purchase #7 $203.99   5.150%   $214.4955   $214.50   $214.50   $214.50  
  7 purchase totals = $1,151.56       $1,261.4687   $1,261.47   $1,261.45   $1,261.50