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 $146.56   13.847%   $166.8542   $166.85   $166.85   $166.90  
  Purchase #2 $27.70   5.595%   $29.2498   $29.25   $29.25   $29.20  
  Purchase #3 $30.87   13.859%   $35.1483   $35.15   $35.15   $35.10  
  Purchase #4 $124.67   8.533%   $135.3081   $135.31   $135.30   $135.30  
  Purchase #5 $231.31   13.601%   $262.7705   $262.77   $262.75   $262.80  
  Purchase #6 $211.89   11.130%   $235.4734   $235.47   $235.45   $235.50  
  Purchase #7 $186.87   8.225%   $202.2401   $202.24   $202.25   $202.20  
  7 purchase totals = $959.87       $1,067.0444   $1,067.04   $1,067.00   $1,067.00