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 $154.27   4.691%   $161.5068   $161.51   $161.50   $161.50  
  Purchase #2 $124.81   6.524%   $132.9526   $132.95   $132.95   $133.00  
  Purchase #3 $170.81   13.555%   $193.9633   $193.96   $193.95   $194.00  
  Purchase #4 $146.25   13.708%   $166.298   $166.30   $166.30   $166.30  
  Purchase #5 $49.71   3.257%   $51.3291   $51.33   $51.35   $51.30  
  Purchase #6 $142.82   3.836%   $148.2986   $148.30   $148.30   $148.30  
  Purchase #7 $152.30   9.602%   $166.9238   $166.92   $166.90   $166.90  
  7 purchase totals = $940.97       $1,021.2722   $1,021.27   $1,021.25   $1,021.30