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 $44.46   11.471%   $49.56   $49.56   $49.55   $49.60  
  Purchase #2 $177.81   11.838%   $198.8591   $198.86   $198.85   $198.90  
  Purchase #3 $240.47   3.755%   $249.4996   $249.50   $249.50   $249.50  
  Purchase #4 $26.40   4.658%   $27.6297   $27.63   $27.65   $27.60  
  Purchase #5 $9.67   12.446%   $10.8735   $10.87   $10.85   $10.90  
  Purchase #6 $98.75   13.376%   $111.9588   $111.96   $111.95   $112.00  
  Purchase #7 $72.87   4.612%   $76.2308   $76.23   $76.25   $76.20  
  7 purchase totals = $670.43       $724.6115   $724.61   $724.60   $724.70