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 $202.44   3.126%   $208.7683   $208.77   $208.75   $208.80  
  Purchase #2 $148.44   7.859%   $160.1059   $160.11   $160.10   $160.10  
  Purchase #3 $188.78   9.392%   $206.5102   $206.51   $206.50   $206.50  
  Purchase #4 $190.74   8.783%   $207.4927   $207.49   $207.50   $207.50  
  Purchase #5 $234.74   11.582%   $261.9276   $261.93   $261.95   $261.90  
  Purchase #6 $224.47   9.699%   $246.2413   $246.24   $246.25   $246.20  
  Purchase #7 $60.89   8.332%   $65.9634   $65.96   $65.95   $66.00  
  7 purchase totals = $1,250.50       $1,357.0094   $1,357.01   $1,357.00   $1,357.00