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 $85.86   7.841%   $92.5923   $92.59   $92.60   $92.60  
  Purchase #2 $32.56   8.112%   $35.2013   $35.20   $35.20   $35.20  
  Purchase #3 $194.29   6.673%   $207.255   $207.26   $207.25   $207.30  
  Purchase #4 $81.39   9.430%   $89.0651   $89.07   $89.05   $89.10  
  Purchase #5 $179.88   6.287%   $191.1891   $191.19   $191.20   $191.20  
  Purchase #6 $77.45   7.712%   $83.4229   $83.42   $83.40   $83.40  
  Purchase #7 $91.38   7.128%   $97.8936   $97.89   $97.90   $97.90  
  7 purchase totals = $742.81       $796.6193   $796.62   $796.60   $796.70