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 $161.65   8.614%   $175.5745   $175.57   $175.55   $175.60  
  Purchase #2 $217.96   6.417%   $231.9465   $231.95   $231.95   $231.90  
  Purchase #3 $240.64   5.664%   $254.2698   $254.27   $254.25   $254.30  
  Purchase #4 $188.46   5.193%   $198.2467   $198.25   $198.25   $198.20  
  Purchase #5 $55.95   7.701%   $60.2587   $60.26   $60.25   $60.30  
  Purchase #6 $113.73   8.363%   $123.2412   $123.24   $123.25   $123.20  
  Purchase #7 $222.70   6.254%   $236.6277   $236.63   $236.65   $236.60  
  7 purchase totals = $1,201.09       $1,280.1651   $1,280.17   $1,280.15   $1,280.10