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 $242.66   8.245%   $262.6673   $262.67   $262.65   $262.70  
  Purchase #2 $175.62   5.679%   $185.5935   $185.59   $185.60   $185.60  
  Purchase #3 $130.59   10.840%   $144.746   $144.75   $144.75   $144.70  
  Purchase #4 $242.76   11.139%   $269.801   $269.80   $269.80   $269.80  
  Purchase #5 $228.83   11.338%   $254.7747   $254.77   $254.75   $254.80  
  Purchase #6 $133.70   9.693%   $146.6595   $146.66   $146.65   $146.70  
  Purchase #7 $84.27   5.538%   $88.9369   $88.94   $88.95   $88.90  
  7 purchase totals = $1,238.43       $1,353.1789   $1,353.18   $1,353.15   $1,353.20