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 $10.31   3.556%   $10.6766   $10.68   $10.70   $10.70  
  Purchase #2 $193.48   3.579%   $200.4046   $200.40   $200.40   $200.40  
  Purchase #3 $6.82   4.544%   $7.1299   $7.13   $7.15   $7.10  
  Purchase #4 $84.88   13.218%   $96.0994   $96.10   $96.10   $96.10  
  Purchase #5 $129.45   8.733%   $140.7549   $140.75   $140.75   $140.80  
  Purchase #6 $26.57   4.512%   $27.7688   $27.77   $27.75   $27.80  
  Purchase #7 $177.83   5.376%   $187.3901   $187.39   $187.40   $187.40  
  7 purchase totals = $629.34       $670.2243   $670.22   $670.25   $670.30