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 $211.34   13.425%   $239.7124   $239.71   $239.70   $239.70  
  Purchase #2 $203.91   5.134%   $214.3787   $214.38   $214.40   $214.40  
  Purchase #3 $21.55   9.563%   $23.6108   $23.61   $23.60   $23.60  
  Purchase #4 $197.66   6.198%   $209.911   $209.91   $209.90   $209.90  
  Purchase #5 $64.49   11.493%   $71.9018   $71.90   $71.90   $71.90  
  Purchase #6 $51.32   7.168%   $54.9986   $55.00   $55.00   $55.00  
  Purchase #7 $226.94   8.360%   $245.9122   $245.91   $245.90   $245.90  
  7 purchase totals = $977.21       $1,060.4255   $1,060.42   $1,060.40   $1,060.40