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 $16.30   13.173%   $18.4472   $18.45   $18.45   $18.40  
  Purchase #2 $39.25   13.334%   $44.4836   $44.48   $44.50   $44.50  
  Purchase #3 $81.56   12.103%   $91.4312   $91.43   $91.45   $91.40  
  Purchase #4 $22.61   5.120%   $23.7676   $23.77   $23.75   $23.80  
  Purchase #5 $67.44   13.334%   $76.4324   $76.43   $76.45   $76.40  
  Purchase #6 $35.88   3.115%   $36.9977   $37.00   $37.00   $37.00  
  Purchase #7 $176.91   8.856%   $192.5771   $192.58   $192.60   $192.60  
  7 purchase totals = $439.95       $484.1368   $484.14   $484.20   $484.10