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 $239.93   8.269%   $259.7698   $259.77   $259.75   $259.80  
  Purchase #2 $196.34   13.189%   $222.2353   $222.24   $222.25   $222.20  
  Purchase #3 $196.43   11.172%   $218.3752   $218.38   $218.40   $218.40  
  Purchase #4 $239.76   11.544%   $267.4379   $267.44   $267.45   $267.40  
  Purchase #5 $57.98   5.795%   $61.3399   $61.34   $61.35   $61.30  
  Purchase #6 $18.33   8.344%   $19.8595   $19.86   $19.85   $19.90  
  Purchase #7 $192.34   4.773%   $201.5204   $201.52   $201.50   $201.50  
  7 purchase totals = $1,141.11       $1,250.5380   $1,250.55   $1,250.55   $1,250.50