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 $84.89   11.155%   $94.3595   $94.36   $94.35   $94.40  
  Purchase #2 $195.71   6.701%   $208.8245   $208.82   $208.80   $208.80  
  Purchase #3 $53.70   4.720%   $56.2346   $56.23   $56.25   $56.20  
  Purchase #4 $104.60   7.634%   $112.5852   $112.59   $112.60   $112.60  
  Purchase #5 $93.70   10.402%   $103.4467   $103.45   $103.45   $103.40  
  Purchase #6 $167.76   9.119%   $183.058   $183.06   $183.05   $183.10  
  Purchase #7 $73.72   9.444%   $80.6821   $80.68   $80.70   $80.70  
  7 purchase totals = $774.08       $839.1906   $839.19   $839.20   $839.20