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 $126.81   3.403%   $131.1253   $131.13   $131.15   $131.10  
  Purchase #2 $95.98   9.605%   $105.1989   $105.20   $105.20   $105.20  
  Purchase #3 $220.26   7.397%   $236.5526   $236.55   $236.55   $236.60  
  Purchase #4 $211.35   7.819%   $227.8755   $227.88   $227.90   $227.90  
  Purchase #5 $249.61   5.460%   $263.2387   $263.24   $263.25   $263.20  
  Purchase #6 $203.59   3.679%   $211.0801   $211.08   $211.10   $211.10  
  Purchase #7 $164.64   8.676%   $178.9242   $178.92   $178.90   $178.90  
  7 purchase totals = $1,272.24       $1,353.9953   $1,354.00   $1,354.05   $1,354.00