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 $81.26   13.632%   $92.3374   $92.34   $92.35   $92.30  
  Purchase #2 $67.98   8.221%   $73.5686   $73.57   $73.55   $73.60  
  Purchase #3 $52.74   13.762%   $59.9981   $60.00   $60.00   $60.00  
  Purchase #4 $64.73   8.208%   $70.043   $70.04   $70.05   $70.00  
  Purchase #5 $240.91   3.139%   $248.4722   $248.47   $248.45   $248.50  
  Purchase #6 $160.46   11.376%   $178.7139   $178.71   $178.70   $178.70  
  Purchase #7 $11.82   12.241%   $13.2669   $13.27   $13.25   $13.30  
  7 purchase totals = $679.90       $736.4001   $736.40   $736.35   $736.40