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 $188.26   13.819%   $214.2756   $214.28   $214.30   $214.30  
  Purchase #2 $131.76   8.293%   $142.6869   $142.69   $142.70   $142.70  
  Purchase #3 $114.74   10.624%   $126.93   $126.93   $126.95   $126.90  
  Purchase #4 $28.76   4.326%   $30.0042   $30.00   $30.00   $30.00  
  Purchase #5 $42.89   12.463%   $48.2354   $48.24   $48.25   $48.20  
  Purchase #6 $190.33   7.690%   $204.9664   $204.97   $204.95   $205.00  
  Purchase #7 $235.81   6.301%   $250.6684   $250.67   $250.65   $250.70  
  7 purchase totals = $932.55       $1,017.7669   $1,017.78   $1,017.80   $1,017.80