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 $235.71   6.767%   $251.6605   $251.66   $251.65   $251.70  
  Purchase #2 $27.68   10.559%   $30.6027   $30.60   $30.60   $30.60  
  Purchase #3 $95.58   12.647%   $107.668   $107.67   $107.65   $107.70  
  Purchase #4 $59.69   7.455%   $64.1399   $64.14   $64.15   $64.10  
  Purchase #5 $70.25   3.321%   $72.583   $72.58   $72.60   $72.60  
  Purchase #6 $226.55   7.431%   $243.3849   $243.38   $243.40   $243.40  
  Purchase #7 $236.45   12.749%   $266.595   $266.60   $266.60   $266.60  
  7 purchase totals = $951.91       $1,036.6340   $1,036.63   $1,036.65   $1,036.70