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 $244.62   3.811%   $253.9425   $253.94   $253.95   $253.90  
  Purchase #2 $240.89   10.307%   $265.7185   $265.72   $265.70   $265.70  
  Purchase #3 $234.53   7.800%   $252.8233   $252.82   $252.80   $252.80  
  Purchase #4 $21.51   9.424%   $23.5371   $23.54   $23.55   $23.50  
  Purchase #5 $227.33   13.792%   $258.6834   $258.68   $258.70   $258.70  
  Purchase #6 $234.66   10.482%   $259.2571   $259.26   $259.25   $259.30  
  Purchase #7 $57.34   6.187%   $60.8876   $60.89   $60.90   $60.90  
  7 purchase totals = $1,260.88       $1,374.8495   $1,374.85   $1,374.85   $1,374.80