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 $47.43   5.418%   $49.9998   $50.00   $50.00   $50.00  
  Purchase #2 $74.93   12.173%   $84.0512   $84.05   $84.05   $84.10  
  Purchase #3 $89.47   11.812%   $100.0382   $100.04   $100.05   $100.00  
  Purchase #4 $78.75   3.501%   $81.507   $81.51   $81.50   $81.50  
  Purchase #5 $94.31   8.639%   $102.4574   $102.46   $102.45   $102.50  
  Purchase #6 $104.86   10.280%   $115.6396   $115.64   $115.65   $115.60  
  Purchase #7 $109.86   10.544%   $121.4436   $121.44   $121.45   $121.40  
  7 purchase totals = $599.61       $655.1368   $655.14   $655.15   $655.10