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 $154.53   6.733%   $164.9345   $164.93   $164.95   $164.90  
  Purchase #2 $190.74   12.554%   $214.6855   $214.69   $214.70   $214.70  
  Purchase #3 $117.86   6.579%   $125.614   $125.61   $125.60   $125.60  
  Purchase #4 $56.29   11.714%   $62.8838   $62.88   $62.90   $62.90  
  Purchase #5 $26.99   5.378%   $28.4415   $28.44   $28.45   $28.40  
  Purchase #6 $22.72   6.509%   $24.1988   $24.20   $24.20   $24.20  
  Purchase #7 $206.62   13.281%   $234.0612   $234.06   $234.05   $234.10  
  7 purchase totals = $775.75       $854.8193   $854.81   $854.85   $854.80