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 $73.34   12.194%   $82.2831   $82.28   $82.30   $82.30  
  Purchase #2 $242.62   6.751%   $258.9993   $259.00   $259.00   $259.00  
  Purchase #3 $26.64   13.523%   $30.2425   $30.24   $30.25   $30.20  
  Purchase #4 $77.74   6.318%   $82.6516   $82.65   $82.65   $82.70  
  Purchase #5 $24.45   7.422%   $26.2647   $26.26   $26.25   $26.30  
  Purchase #6 $152.97   11.618%   $170.7421   $170.74   $170.75   $170.70  
  Purchase #7 $115.65   13.719%   $131.516   $131.52   $131.50   $131.50  
  7 purchase totals = $713.41       $782.6993   $782.69   $782.70   $782.70