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 $246.76   8.636%   $268.0702   $268.07   $268.05   $268.10  
  Purchase #2 $135.37   9.253%   $147.8958   $147.90   $147.90   $147.90  
  Purchase #3 $232.87   10.710%   $257.8104   $257.81   $257.80   $257.80  
  Purchase #4 $76.52   11.728%   $85.4943   $85.49   $85.50   $85.50  
  Purchase #5 $84.30   13.578%   $95.7463   $95.75   $95.75   $95.70  
  Purchase #6 $232.73   6.312%   $247.4199   $247.42   $247.40   $247.40  
  Purchase #7 $144.54   8.411%   $156.6973   $156.70   $156.70   $156.70  
  7 purchase totals = $1,153.09       $1,259.1342   $1,259.14   $1,259.10   $1,259.10