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 $222.95   5.422%   $235.0383   $235.04   $235.05   $235.00  
  Purchase #2 $178.85   8.214%   $193.5407   $193.54   $193.55   $193.50  
  Purchase #3 $27.29   12.533%   $30.7103   $30.71   $30.70   $30.70  
  Purchase #4 $122.27   13.267%   $138.4916   $138.49   $138.50   $138.50  
  Purchase #5 $243.86   12.439%   $274.1937   $274.19   $274.20   $274.20  
  Purchase #6 $156.42   13.418%   $177.4084   $177.41   $177.40   $177.40  
  Purchase #7 $5.72   4.673%   $5.9873   $5.99   $6.00   $6.00  
  7 purchase totals = $957.36       $1,055.3703   $1,055.37   $1,055.40   $1,055.30