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 $47.87   5.501%   $50.5033   $50.50   $50.50   $50.50  
  Purchase #2 $122.79   5.629%   $129.7018   $129.70   $129.70   $129.70  
  Purchase #3 $158.35   3.114%   $163.281   $163.28   $163.30   $163.30  
  Purchase #4 $81.59   6.517%   $86.9072   $86.91   $86.90   $86.90  
  Purchase #5 $211.87   12.682%   $238.7394   $238.74   $238.75   $238.70  
  Purchase #6 $136.92   5.826%   $144.897   $144.90   $144.90   $144.90  
  Purchase #7 $60.26   11.777%   $67.3568   $67.36   $67.35   $67.40  
  7 purchase totals = $819.65       $881.3865   $881.39   $881.40   $881.40