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 $63.38   3.586%   $65.6528   $65.65   $65.65   $65.70  
  Purchase #2 $53.38   6.238%   $56.7098   $56.71   $56.70   $56.70  
  Purchase #3 $26.73   12.869%   $30.1699   $30.17   $30.15   $30.20  
  Purchase #4 $46.26   11.691%   $51.6683   $51.67   $51.65   $51.70  
  Purchase #5 $247.69   9.835%   $272.0503   $272.05   $272.05   $272.10  
  Purchase #6 $210.51   8.238%   $227.8518   $227.85   $227.85   $227.90  
  Purchase #7 $143.91   9.362%   $157.3829   $157.38   $157.40   $157.40  
  7 purchase totals = $791.86       $861.4858   $861.48   $861.45   $861.70