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 $199.65   13.702%   $227.006   $227.01   $227.00   $227.00  
  Purchase #2 $23.65   13.355%   $26.8085   $26.81   $26.80   $26.80  
  Purchase #3 $242.90   10.667%   $268.8101   $268.81   $268.80   $268.80  
  Purchase #4 $125.79   6.778%   $134.316   $134.32   $134.30   $134.30  
  Purchase #5 $174.31   11.172%   $193.7839   $193.78   $193.80   $193.80  
  Purchase #6 $208.63   13.368%   $236.5197   $236.52   $236.50   $236.50  
  Purchase #7 $132.85   13.619%   $150.9428   $150.94   $150.95   $150.90  
  7 purchase totals = $1,107.78       $1,238.1870   $1,238.19   $1,238.15   $1,238.10