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 $55.75   12.389%   $62.6569   $62.66   $62.65   $62.70  
  Purchase #2 $55.83   8.436%   $60.5398   $60.54   $60.55   $60.50  
  Purchase #3 $25.49   5.465%   $26.883   $26.88   $26.90   $26.90  
  Purchase #4 $183.68   7.834%   $198.0695   $198.07   $198.05   $198.10  
  Purchase #5 $57.52   9.571%   $63.0252   $63.03   $63.05   $63.00  
  Purchase #6 $184.76   7.561%   $198.7297   $198.73   $198.75   $198.70  
  Purchase #7 $174.74   6.813%   $186.645   $186.65   $186.65   $186.60  
  7 purchase totals = $737.77       $796.5491   $796.56   $796.60   $796.50