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 $60.58   10.110%   $66.7046   $66.70   $66.70   $66.70  
  Purchase #2 $224.77   10.366%   $248.0697   $248.07   $248.05   $248.10  
  Purchase #3 $151.62   4.137%   $157.8925   $157.89   $157.90   $157.90  
  Purchase #4 $169.94   3.347%   $175.6279   $175.63   $175.65   $175.60  
  Purchase #5 $137.50   10.595%   $152.0681   $152.07   $152.05   $152.10  
  Purchase #6 $198.85   9.482%   $217.705   $217.71   $217.70   $217.70  
  Purchase #7 $243.84   6.210%   $258.9825   $258.98   $259.00   $259.00  
  7 purchase totals = $1,187.10       $1,277.0503   $1,277.05   $1,277.05   $1,277.10