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 $59.25   6.838%   $63.3015   $63.30   $63.30   $63.30  
  Purchase #2 $42.31   7.630%   $45.5383   $45.54   $45.55   $45.50  
  Purchase #3 $109.99   6.566%   $117.2119   $117.21   $117.20   $117.20  
  Purchase #4 $144.78   11.267%   $161.0924   $161.09   $161.10   $161.10  
  Purchase #5 $124.49   7.219%   $133.4769   $133.48   $133.50   $133.50  
  Purchase #6 $209.45   12.200%   $235.0029   $235.00   $235.00   $235.00  
  Purchase #7 $82.36   4.779%   $86.296   $86.30   $86.30   $86.30  
  7 purchase totals = $772.63       $841.9199   $841.92   $841.95   $841.90