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 $224.40   9.546%   $245.8212   $245.82   $245.80   $245.80  
  Purchase #2 $177.31   13.522%   $201.2859   $201.29   $201.30   $201.30  
  Purchase #3 $184.40   3.591%   $191.0218   $191.02   $191.00   $191.00  
  Purchase #4 $25.76   4.661%   $26.9607   $26.96   $26.95   $27.00  
  Purchase #5 $23.69   13.351%   $26.8529   $26.85   $26.85   $26.90  
  Purchase #6 $234.73   6.500%   $249.9875   $249.99   $250.00   $250.00  
  Purchase #7 $49.36   3.845%   $51.2579   $51.26   $51.25   $51.30  
  7 purchase totals = $919.65       $993.1879   $993.19   $993.15   $993.30