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 $242.58   10.464%   $267.9636   $267.96   $267.95   $268.00  
  Purchase #2 $68.86   8.326%   $74.5933   $74.59   $74.60   $74.60  
  Purchase #3 $235.68   10.203%   $259.7264   $259.73   $259.75   $259.70  
  Purchase #4 $55.77   10.201%   $61.4591   $61.46   $61.45   $61.50  
  Purchase #5 $193.69   7.623%   $208.455   $208.46   $208.45   $208.50  
  Purchase #6 $168.89   8.814%   $183.776   $183.78   $183.80   $183.80  
  Purchase #7 $8.57   4.663%   $8.9696   $8.97   $8.95   $9.00  
  7 purchase totals = $974.04       $1,064.9430   $1,064.95   $1,064.95   $1,065.10