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 $61.46   3.379%   $63.5367   $63.54   $63.55   $63.50  
  Purchase #2 $141.42   9.638%   $155.0501   $155.05   $155.05   $155.10  
  Purchase #3 $72.96   11.809%   $81.5758   $81.58   $81.60   $81.60  
  Purchase #4 $206.99   3.593%   $214.4272   $214.43   $214.45   $214.40  
  Purchase #5 $67.86   11.309%   $75.5343   $75.53   $75.55   $75.50  
  Purchase #6 $154.56   4.121%   $160.9294   $160.93   $160.95   $160.90  
  Purchase #7 $64.84   9.646%   $71.0945   $71.09   $71.10   $71.10  
  7 purchase totals = $770.09       $822.1480   $822.15   $822.25   $822.10