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 $176.43   8.405%   $191.2589   $191.26   $191.25   $191.30  
  Purchase #2 $93.97   8.408%   $101.871   $101.87   $101.85   $101.90  
  Purchase #3 $60.46   8.507%   $65.6033   $65.60   $65.60   $65.60  
  Purchase #4 $19.76   12.298%   $22.1901   $22.19   $22.20   $22.20  
  Purchase #5 $101.31   12.715%   $114.1916   $114.19   $114.20   $114.20  
  Purchase #6 $76.57   3.535%   $79.2767   $79.28   $79.30   $79.30  
  Purchase #7 $106.98   13.784%   $121.7261   $121.73   $121.75   $121.70  
  7 purchase totals = $635.48       $696.1177   $696.12   $696.15   $696.20