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 $162.41   12.848%   $183.2764   $183.28   $183.30   $183.30  
  Purchase #2 $176.43   9.438%   $193.0815   $193.08   $193.10   $193.10  
  Purchase #3 $77.52   8.866%   $84.3929   $84.39   $84.40   $84.40  
  Purchase #4 $239.93   8.750%   $260.9239   $260.92   $260.90   $260.90  
  Purchase #5 $136.27   11.204%   $151.5377   $151.54   $151.55   $151.50  
  Purchase #6 $117.45   13.507%   $133.314   $133.31   $133.30   $133.30  
  Purchase #7 $193.28   12.209%   $216.8776   $216.88   $216.90   $216.90  
  7 purchase totals = $1,103.29       $1,223.4040   $1,223.40   $1,223.45   $1,223.40