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 $209.50   12.662%   $236.0269   $236.03   $236.05   $236.00  
  Purchase #2 $156.30   3.137%   $161.2031   $161.20   $161.20   $161.20  
  Purchase #3 $228.59   5.206%   $240.4904   $240.49   $240.50   $240.50  
  Purchase #4 $158.81   3.294%   $164.0412   $164.04   $164.05   $164.00  
  Purchase #5 $25.35   3.586%   $26.2591   $26.26   $26.25   $26.30  
  Purchase #6 $218.77   13.371%   $248.0217   $248.02   $248.00   $248.00  
  Purchase #7 $181.49   7.438%   $194.9892   $194.99   $195.00   $195.00  
  7 purchase totals = $1,178.81       $1,271.0316   $1,271.03   $1,271.05   $1,271.00