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 $86.29   13.608%   $98.0323   $98.03   $98.05   $98.00  
  Purchase #2 $74.64   11.371%   $83.1273   $83.13   $83.15   $83.10  
  Purchase #3 $242.94   5.853%   $257.1593   $257.16   $257.15   $257.20  
  Purchase #4 $202.66   11.383%   $225.7288   $225.73   $225.75   $225.70  
  Purchase #5 $163.71   5.430%   $172.5995   $172.60   $172.60   $172.60  
  Purchase #6 $246.34   12.196%   $276.3836   $276.38   $276.40   $276.40  
  Purchase #7 $113.39   13.337%   $128.5128   $128.51   $128.50   $128.50  
  7 purchase totals = $1,129.97       $1,241.5436   $1,241.54   $1,241.60   $1,241.50