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 $76.58   12.593%   $86.2237   $86.22   $86.20   $86.20  
  Purchase #2 $166.95   4.567%   $174.5746   $174.57   $174.55   $174.60  
  Purchase #3 $136.81   7.548%   $147.1364   $147.14   $147.15   $147.10  
  Purchase #4 $166.64   13.144%   $188.5432   $188.54   $188.55   $188.50  
  Purchase #5 $216.43   8.132%   $234.0301   $234.03   $234.05   $234.00  
  Purchase #6 $73.48   4.634%   $76.8851   $76.89   $76.90   $76.90  
  Purchase #7 $105.69   11.108%   $117.43   $117.43   $117.45   $117.40  
  7 purchase totals = $942.58       $1,024.8231   $1,024.82   $1,024.85   $1,024.70