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 $124.87   8.711%   $135.7474   $135.75   $135.75   $135.70  
  Purchase #2 $65.29   6.676%   $69.6488   $69.65   $69.65   $69.60  
  Purchase #3 $143.57   6.605%   $153.0528   $153.05   $153.05   $153.10  
  Purchase #4 $225.87   10.602%   $249.8167   $249.82   $249.80   $249.80  
  Purchase #5 $242.46   5.562%   $255.9456   $255.95   $255.95   $255.90  
  Purchase #6 $151.82   4.633%   $158.8538   $158.85   $158.85   $158.90  
  Purchase #7 $215.89   9.700%   $236.8313   $236.83   $236.85   $236.80  
  7 purchase totals = $1,169.77       $1,259.8964   $1,259.90   $1,259.90   $1,259.80