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 $166.38   10.566%   $183.9597   $183.96   $183.95   $184.00  
  Purchase #2 $67.62   12.790%   $76.2686   $76.27   $76.25   $76.30  
  Purchase #3 $41.25   10.285%   $45.4926   $45.49   $45.50   $45.50  
  Purchase #4 $207.94   6.559%   $221.5788   $221.58   $221.60   $221.60  
  Purchase #5 $74.63   12.581%   $84.0192   $84.02   $84.00   $84.00  
  Purchase #6 $112.70   6.372%   $119.8812   $119.88   $119.90   $119.90  
  Purchase #7 $227.39   8.743%   $247.2707   $247.27   $247.25   $247.30  
  7 purchase totals = $897.91       $978.4708   $978.47   $978.45   $978.60