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 $182.42   13.486%   $207.0212   $207.02   $207.00   $207.00  
  Purchase #2 $87.72   7.216%   $94.0499   $94.05   $94.05   $94.00  
  Purchase #3 $196.28   12.775%   $221.3548   $221.35   $221.35   $221.40  
  Purchase #4 $95.49   13.364%   $108.2513   $108.25   $108.25   $108.30  
  Purchase #5 $146.73   4.710%   $153.641   $153.64   $153.65   $153.60  
  Purchase #6 $196.26   3.131%   $202.4049   $202.40   $202.40   $202.40  
  Purchase #7 $234.66   8.564%   $254.7563   $254.76   $254.75   $254.80  
  7 purchase totals = $1,139.56       $1,241.4794   $1,241.47   $1,241.45   $1,241.50