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 $56.51   8.776%   $61.4693   $61.47   $61.45   $61.50  
  Purchase #2 $155.50   10.828%   $172.3375   $172.34   $172.35   $172.30  
  Purchase #3 $245.26   8.624%   $266.4112   $266.41   $266.40   $266.40  
  Purchase #4 $196.45   3.106%   $202.5517   $202.55   $202.55   $202.60  
  Purchase #5 $69.66   7.851%   $75.129   $75.13   $75.15   $75.10  
  Purchase #6 $41.45   7.531%   $44.5716   $44.57   $44.55   $44.60  
  Purchase #7 $27.90   13.627%   $31.7019   $31.70   $31.70   $31.70  
  7 purchase totals = $792.73       $854.1722   $854.17   $854.15   $854.20