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 $242.78   10.384%   $267.9903   $267.99   $268.00   $268.00  
  Purchase #2 $166.64   7.743%   $179.5429   $179.54   $179.55   $179.50  
  Purchase #3 $163.64   11.444%   $182.367   $182.37   $182.35   $182.40  
  Purchase #4 $247.47   3.453%   $256.0151   $256.02   $256.00   $256.00  
  Purchase #5 $88.86   8.873%   $96.7445   $96.74   $96.75   $96.70  
  Purchase #6 $146.38   5.553%   $154.5085   $154.51   $154.50   $154.50  
  Purchase #7 $22.50   3.750%   $23.3438   $23.34   $23.35   $23.30  
  7 purchase totals = $1,078.27       $1,160.5121   $1,160.51   $1,160.50   $1,160.40