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 $232.42   7.583%   $250.0444   $250.04   $250.05   $250.00  
  Purchase #2 $249.36   12.469%   $280.4527   $280.45   $280.45   $280.50  
  Purchase #3 $55.46   13.580%   $62.9915   $62.99   $63.00   $63.00  
  Purchase #4 $159.41   8.752%   $173.3616   $173.36   $173.35   $173.40  
  Purchase #5 $42.99   8.495%   $46.642   $46.64   $46.65   $46.60  
  Purchase #6 $155.72   6.199%   $165.3731   $165.37   $165.35   $165.40  
  Purchase #7 $22.49   8.469%   $24.3947   $24.39   $24.40   $24.40  
  7 purchase totals = $917.85       $1,003.2600   $1,003.24   $1,003.25   $1,003.30