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 $62.99   10.156%   $69.3873   $69.39   $69.40   $69.40  
  Purchase #2 $201.35   3.448%   $208.2925   $208.29   $208.30   $208.30  
  Purchase #3 $225.56   13.734%   $256.5384   $256.54   $256.55   $256.50  
  Purchase #4 $31.61   5.310%   $33.2885   $33.29   $33.30   $33.30  
  Purchase #5 $241.69   4.707%   $253.0663   $253.07   $253.05   $253.10  
  Purchase #6 $47.67   9.698%   $52.293   $52.29   $52.30   $52.30  
  Purchase #7 $32.38   4.403%   $33.8057   $33.81   $33.80   $33.80  
  7 purchase totals = $843.25       $906.6717   $906.68   $906.70   $906.70