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 $248.94   5.622%   $262.9354   $262.94   $262.95   $262.90  
  Purchase #2 $191.28   11.306%   $212.9061   $212.91   $212.90   $212.90  
  Purchase #3 $27.92   5.430%   $29.4361   $29.44   $29.45   $29.40  
  Purchase #4 $51.93   11.110%   $57.6994   $57.70   $57.70   $57.70  
  Purchase #5 $175.33   10.424%   $193.6064   $193.61   $193.60   $193.60  
  Purchase #6 $210.53   13.169%   $238.2547   $238.25   $238.25   $238.30  
  Purchase #7 $190.62   10.817%   $211.2394   $211.24   $211.25   $211.20  
  7 purchase totals = $1,096.55       $1,206.0775   $1,206.09   $1,206.10   $1,206.00