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 $180.81   11.354%   $201.3392   $201.34   $201.35   $201.30  
  Purchase #2 $177.52   12.321%   $199.3922   $199.39   $199.40   $199.40  
  Purchase #3 $216.55   7.648%   $233.1117   $233.11   $233.10   $233.10  
  Purchase #4 $26.84   3.240%   $27.7096   $27.71   $27.70   $27.70  
  Purchase #5 $233.53   9.425%   $255.5402   $255.54   $255.55   $255.50  
  Purchase #6 $236.83   6.726%   $252.7592   $252.76   $252.75   $252.80  
  Purchase #7 $161.36   13.179%   $182.6256   $182.63   $182.65   $182.60  
  7 purchase totals = $1,233.44       $1,352.4777   $1,352.48   $1,352.50   $1,352.40