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 $124.48   8.727%   $135.3434   $135.34   $135.35   $135.30  
  Purchase #2 $71.93   13.309%   $81.5032   $81.50   $81.50   $81.50  
  Purchase #3 $148.47   12.866%   $167.5722   $167.57   $167.55   $167.60  
  Purchase #4 $178.38   10.126%   $196.4428   $196.44   $196.45   $196.40  
  Purchase #5 $211.61   11.831%   $236.6456   $236.65   $236.65   $236.60  
  Purchase #6 $179.27   4.689%   $187.676   $187.68   $187.70   $187.70  
  Purchase #7 $148.68   12.321%   $166.9989   $167.00   $167.00   $167.00  
  7 purchase totals = $1,062.82       $1,172.1821   $1,172.18   $1,172.20   $1,172.10