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 $229.72   10.553%   $253.9624   $253.96   $253.95   $254.00  
  Purchase #2 $150.85   13.108%   $170.6234   $170.62   $170.60   $170.60  
  Purchase #3 $231.34   9.671%   $253.7129   $253.71   $253.70   $253.70  
  Purchase #4 $71.27   9.836%   $78.2801   $78.28   $78.30   $78.30  
  Purchase #5 $94.77   13.173%   $107.2541   $107.25   $107.25   $107.30  
  Purchase #6 $140.38   12.216%   $157.5288   $157.53   $157.55   $157.50  
  Purchase #7 $46.36   12.598%   $52.2004   $52.20   $52.20   $52.20  
  7 purchase totals = $964.69       $1,073.5621   $1,073.55   $1,073.55   $1,073.60