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 $183.30   13.743%   $208.4909   $208.49   $208.50   $208.50  
  Purchase #2 $233.44   3.130%   $240.7467   $240.75   $240.75   $240.70  
  Purchase #3 $67.94   8.337%   $73.6042   $73.60   $73.60   $73.60  
  Purchase #4 $149.29   13.478%   $169.4113   $169.41   $169.40   $169.40  
  Purchase #5 $249.33   11.383%   $277.7112   $277.71   $277.70   $277.70  
  Purchase #6 $115.50   5.173%   $121.4748   $121.47   $121.45   $121.50  
  Purchase #7 $55.76   8.811%   $60.673   $60.67   $60.65   $60.70  
  7 purchase totals = $1,054.56       $1,152.1121   $1,152.10   $1,152.05   $1,152.10