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 $76.39   10.266%   $84.2322   $84.23   $84.25   $84.20  
  Purchase #2 $90.57   7.538%   $97.3972   $97.40   $97.40   $97.40  
  Purchase #3 $45.75   4.785%   $47.9391   $47.94   $47.95   $47.90  
  Purchase #4 $125.28   4.198%   $130.5393   $130.54   $130.55   $130.50  
  Purchase #5 $192.95   11.370%   $214.8884   $214.89   $214.90   $214.90  
  Purchase #6 $52.50   6.777%   $56.0579   $56.06   $56.05   $56.10  
  Purchase #7 $22.45   10.459%   $24.798   $24.80   $24.80   $24.80  
  7 purchase totals = $605.89       $655.8521   $655.86   $655.90   $655.80