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 $86.90   13.309%   $98.4655   $98.47   $98.45   $98.50  
  Purchase #2 $112.70   9.679%   $123.6082   $123.61   $123.60   $123.60  
  Purchase #3 $237.87   11.557%   $265.3606   $265.36   $265.35   $265.40  
  Purchase #4 $125.55   13.574%   $142.5922   $142.59   $142.60   $142.60  
  Purchase #5 $166.84   6.439%   $177.5828   $177.58   $177.60   $177.60  
  Purchase #6 $147.46   6.498%   $157.042   $157.04   $157.05   $157.00  
  Purchase #7 $187.72   7.462%   $201.7277   $201.73   $201.75   $201.70  
  7 purchase totals = $1,065.04       $1,166.3790   $1,166.38   $1,166.40   $1,166.40