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 $59.95   9.505%   $65.6482   $65.65   $65.65   $65.60  
  Purchase #2 $227.42   8.113%   $245.8706   $245.87   $245.85   $245.90  
  Purchase #3 $52.26   6.458%   $55.635   $55.64   $55.65   $55.60  
  Purchase #4 $37.51   13.855%   $42.707   $42.71   $42.70   $42.70  
  Purchase #5 $222.33   13.716%   $252.8248   $252.82   $252.80   $252.80  
  Purchase #6 $147.47   12.709%   $166.212   $166.21   $166.20   $166.20  
  Purchase #7 $109.72   6.779%   $117.1579   $117.16   $117.15   $117.20  
  7 purchase totals = $856.66       $946.0555   $946.06   $946.00   $946.00