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 $85.76   11.189%   $95.3557   $95.36   $95.35   $95.40  
  Purchase #2 $193.67   13.108%   $219.0563   $219.06   $219.05   $219.10  
  Purchase #3 $139.50   6.325%   $148.3234   $148.32   $148.30   $148.30  
  Purchase #4 $129.51   3.532%   $134.0843   $134.08   $134.10   $134.10  
  Purchase #5 $124.75   8.431%   $135.2677   $135.27   $135.25   $135.30  
  Purchase #6 $250.49   3.421%   $259.0593   $259.06   $259.05   $259.10  
  Purchase #7 $69.94   5.595%   $73.8531   $73.85   $73.85   $73.90  
  7 purchase totals = $993.62       $1,064.9998   $1,065.00   $1,064.95   $1,065.20