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 $179.52   12.624%   $202.1826   $202.18   $202.20   $202.20  
  Purchase #2 $114.29   5.250%   $120.2902   $120.29   $120.30   $120.30  
  Purchase #3 $25.64   3.203%   $26.4612   $26.46   $26.45   $26.50  
  Purchase #4 $222.32   10.617%   $245.9237   $245.92   $245.90   $245.90  
  Purchase #5 $126.61   13.649%   $143.891   $143.89   $143.90   $143.90  
  Purchase #6 $160.53   13.694%   $182.513   $182.51   $182.50   $182.50  
  Purchase #7 $46.98   8.328%   $50.8925   $50.89   $50.90   $50.90  
  7 purchase totals = $875.89       $972.1542   $972.14   $972.15   $972.20