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 $163.34   11.873%   $182.7334   $182.73   $182.75   $182.70  
  Purchase #2 $234.95   11.287%   $261.4688   $261.47   $261.45   $261.50  
  Purchase #3 $131.75   12.558%   $148.2952   $148.30   $148.30   $148.30  
  Purchase #4 $162.37   8.283%   $175.8191   $175.82   $175.80   $175.80  
  Purchase #5 $106.81   10.701%   $118.2397   $118.24   $118.25   $118.20  
  Purchase #6 $80.55   12.472%   $90.5962   $90.60   $90.60   $90.60  
  Purchase #7 $64.82   5.295%   $68.2522   $68.25   $68.25   $68.30  
  7 purchase totals = $944.59       $1,045.4046   $1,045.41   $1,045.40   $1,045.40