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 $197.55   9.613%   $216.5405   $216.54   $216.55   $216.50  
  Purchase #2 $155.37   8.536%   $168.6324   $168.63   $168.65   $168.60  
  Purchase #3 $75.32   13.764%   $85.687   $85.69   $85.70   $85.70  
  Purchase #4 $250.65   7.545%   $269.5615   $269.56   $269.55   $269.60  
  Purchase #5 $55.77   3.655%   $57.8084   $57.81   $57.80   $57.80  
  Purchase #6 $202.89   3.846%   $210.6931   $210.69   $210.70   $210.70  
  Purchase #7 $13.95   11.662%   $15.5768   $15.58   $15.60   $15.60  
  7 purchase totals = $951.50       $1,024.4997   $1,024.50   $1,024.55   $1,024.50