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 $162.71   12.411%   $182.9039   $182.90   $182.90   $182.90  
  Purchase #2 $245.39   11.647%   $273.9706   $273.97   $273.95   $274.00  
  Purchase #3 $168.77   13.438%   $191.4493   $191.45   $191.45   $191.40  
  Purchase #4 $84.90   9.649%   $93.092   $93.09   $93.10   $93.10  
  Purchase #5 $8.40   13.759%   $9.5558   $9.56   $9.55   $9.60  
  Purchase #6 $127.71   10.433%   $141.034   $141.03   $141.05   $141.00  
  Purchase #7 $57.28   4.609%   $59.92   $59.92   $59.90   $59.90  
  7 purchase totals = $855.16       $951.9256   $951.92   $951.90   $951.90