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 $52.45   12.293%   $58.8977   $58.90   $58.90   $58.90  
  Purchase #2 $33.95   6.596%   $36.1893   $36.19   $36.20   $36.20  
  Purchase #3 $217.44   4.179%   $226.5268   $226.53   $226.55   $226.50  
  Purchase #4 $199.76   6.462%   $212.6685   $212.67   $212.65   $212.70  
  Purchase #5 $16.37   10.359%   $18.0658   $18.07   $18.05   $18.10  
  Purchase #6 $110.49   4.730%   $115.7162   $115.72   $115.70   $115.70  
  Purchase #7 $102.95   11.135%   $114.4135   $114.41   $114.40   $114.40  
  7 purchase totals = $733.41       $782.4778   $782.49   $782.45   $782.50