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 $47.62   10.501%   $52.6206   $52.62   $52.60   $52.60  
  Purchase #2 $240.95   4.119%   $250.8747   $250.87   $250.85   $250.90  
  Purchase #3 $76.50   5.664%   $80.833   $80.83   $80.85   $80.80  
  Purchase #4 $124.87   8.365%   $135.3154   $135.32   $135.30   $135.30  
  Purchase #5 $82.93   12.510%   $93.3045   $93.30   $93.30   $93.30  
  Purchase #6 $88.45   13.225%   $100.1475   $100.15   $100.15   $100.10  
  Purchase #7 $236.78   5.119%   $248.9008   $248.90   $248.90   $248.90  
  7 purchase totals = $898.10       $961.9965   $961.99   $961.95   $961.90