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 $241.95   10.330%   $266.9434   $266.94   $266.95   $266.90  
  Purchase #2 $103.73   12.468%   $116.6631   $116.66   $116.65   $116.70  
  Purchase #3 $60.58   5.438%   $63.8743   $63.87   $63.85   $63.90  
  Purchase #4 $64.68   13.539%   $73.437   $73.44   $73.45   $73.40  
  Purchase #5 $80.90   8.611%   $87.8663   $87.87   $87.85   $87.90  
  Purchase #6 $110.81   3.165%   $114.3171   $114.32   $114.30   $114.30  
  Purchase #7 $10.51   11.546%   $11.7235   $11.72   $11.70   $11.70  
  7 purchase totals = $673.16       $734.8247   $734.82   $734.75   $734.80