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 $66.34   13.630%   $75.3821   $75.38   $75.40   $75.40  
  Purchase #2 $133.39   8.435%   $144.6414   $144.64   $144.65   $144.60  
  Purchase #3 $44.70   3.446%   $46.2404   $46.24   $46.25   $46.20  
  Purchase #4 $73.69   4.427%   $76.9523   $76.95   $76.95   $77.00  
  Purchase #5 $61.74   6.667%   $65.8562   $65.86   $65.85   $65.90  
  Purchase #6 $208.40   6.591%   $222.1356   $222.14   $222.15   $222.10  
  Purchase #7 $59.99   8.468%   $65.07   $65.07   $65.05   $65.10  
  7 purchase totals = $648.25       $696.2780   $696.28   $696.30   $696.30