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 $98.56   12.859%   $111.2338   $111.23   $111.25   $111.20  
  Purchase #2 $159.87   11.293%   $177.9241   $177.92   $177.90   $177.90  
  Purchase #3 $225.47   12.564%   $253.7981   $253.80   $253.80   $253.80  
  Purchase #4 $59.57   8.646%   $64.7204   $64.72   $64.70   $64.70  
  Purchase #5 $61.61   10.293%   $67.9515   $67.95   $67.95   $68.00  
  Purchase #6 $230.63   4.310%   $240.5702   $240.57   $240.55   $240.60  
  Purchase #7 $92.68   3.123%   $95.5744   $95.57   $95.55   $95.60  
  7 purchase totals = $928.39       $1,011.7725   $1,011.76   $1,011.70   $1,011.80