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 $236.65   13.273%   $268.0606   $268.06   $268.05   $268.10  
  Purchase #2 $49.91   6.735%   $53.2714   $53.27   $53.25   $53.30  
  Purchase #3 $115.29   13.719%   $131.1066   $131.11   $131.10   $131.10  
  Purchase #4 $104.88   10.822%   $116.2301   $116.23   $116.25   $116.20  
  Purchase #5 $114.74   8.146%   $124.0867   $124.09   $124.10   $124.10  
  Purchase #6 $212.58   5.206%   $223.6469   $223.65   $223.65   $223.60  
  Purchase #7 $47.88   4.304%   $49.9408   $49.94   $49.95   $49.90  
  7 purchase totals = $881.93       $966.3431   $966.35   $966.35   $966.30