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 $249.29   5.796%   $263.7388   $263.74   $263.75   $263.70  
  Purchase #2 $193.60   13.217%   $219.1881   $219.19   $219.20   $219.20  
  Purchase #3 $18.47   3.250%   $19.0703   $19.07   $19.05   $19.10  
  Purchase #4 $84.99   9.335%   $92.9238   $92.92   $92.90   $92.90  
  Purchase #5 $245.67   4.793%   $257.445   $257.45   $257.45   $257.40  
  Purchase #6 $190.97   3.434%   $197.5279   $197.53   $197.55   $197.50  
  Purchase #7 $193.25   10.171%   $212.9055   $212.91   $212.90   $212.90  
  7 purchase totals = $1,176.24       $1,262.7994   $1,262.81   $1,262.80   $1,262.70