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 $56.70   10.422%   $62.6093   $62.61   $62.60   $62.60  
  Purchase #2 $136.88   13.188%   $154.9317   $154.93   $154.95   $154.90  
  Purchase #3 $106.87   5.663%   $112.922   $112.92   $112.90   $112.90  
  Purchase #4 $124.81   10.779%   $138.2633   $138.26   $138.25   $138.30  
  Purchase #5 $76.30   11.313%   $84.9318   $84.93   $84.95   $84.90  
  Purchase #6 $14.77   12.253%   $16.5798   $16.58   $16.60   $16.60  
  Purchase #7 $80.61   8.330%   $87.3248   $87.32   $87.30   $87.30  
  7 purchase totals = $596.94       $657.5627   $657.55   $657.55   $657.50