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 $91.80   6.260%   $97.5467   $97.55   $97.55   $97.50  
  Purchase #2 $12.39   9.389%   $13.5533   $13.55   $13.55   $13.60  
  Purchase #3 $127.75   4.225%   $133.1474   $133.15   $133.15   $133.10  
  Purchase #4 $97.89   12.844%   $110.463   $110.46   $110.45   $110.50  
  Purchase #5 $248.56   13.146%   $281.2357   $281.24   $281.25   $281.20  
  Purchase #6 $240.26   10.688%   $265.939   $265.94   $265.95   $265.90  
  Purchase #7 $154.44   13.754%   $175.6817   $175.68   $175.70   $175.70  
  7 purchase totals = $973.09       $1,077.5668   $1,077.57   $1,077.60   $1,077.50