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 $56.27   6.542%   $59.9512   $59.95   $59.95   $60.00  
  Purchase #2 $197.38   5.379%   $207.9971   $208.00   $208.00   $208.00  
  Purchase #3 $126.26   3.838%   $131.1059   $131.11   $131.10   $131.10  
  Purchase #4 $240.81   13.688%   $273.7721   $273.77   $273.75   $273.80  
  Purchase #5 $142.92   3.609%   $148.078   $148.08   $148.10   $148.10  
  Purchase #6 $121.49   13.344%   $137.7016   $137.70   $137.70   $137.70  
  Purchase #7 $17.82   11.746%   $19.9131   $19.91   $19.90   $19.90  
  7 purchase totals = $902.95       $978.5190   $978.52   $978.50   $978.60