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 $113.82   7.682%   $122.5637   $122.56   $122.55   $122.60  
  Purchase #2 $146.63   13.402%   $166.2814   $166.28   $166.30   $166.30  
  Purchase #3 $72.84   9.411%   $79.695   $79.70   $79.70   $79.70  
  Purchase #4 $248.71   9.347%   $271.9569   $271.96   $271.95   $272.00  
  Purchase #5 $162.83   6.581%   $173.5458   $173.55   $173.55   $173.50  
  Purchase #6 $163.40   4.751%   $171.1631   $171.16   $171.15   $171.20  
  Purchase #7 $20.82   7.518%   $22.3852   $22.39   $22.40   $22.40  
  7 purchase totals = $929.05       $1,007.5911   $1,007.60   $1,007.60   $1,007.70