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 $209.71   12.502%   $235.9279   $235.93   $235.95   $235.90  
  Purchase #2 $168.33   9.123%   $183.6867   $183.69   $183.70   $183.70  
  Purchase #3 $158.83   12.622%   $178.8775   $178.88   $178.90   $178.90  
  Purchase #4 $236.61   5.686%   $250.0636   $250.06   $250.05   $250.10  
  Purchase #5 $82.35   9.587%   $90.2449   $90.24   $90.25   $90.20  
  Purchase #6 $68.89   9.145%   $75.19   $75.19   $75.20   $75.20  
  Purchase #7 $168.51   12.162%   $189.0042   $189.00   $189.00   $189.00  
  7 purchase totals = $1,093.23       $1,202.9948   $1,202.99   $1,203.05   $1,203.00