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 $200.62   13.803%   $228.3116   $228.31   $228.30   $228.30  
  Purchase #2 $69.61   7.313%   $74.7006   $74.70   $74.70   $74.70  
  Purchase #3 $239.55   9.660%   $262.6905   $262.69   $262.70   $262.70  
  Purchase #4 $208.74   12.480%   $234.7908   $234.79   $234.80   $234.80  
  Purchase #5 $94.63   4.737%   $99.1126   $99.11   $99.10   $99.10  
  Purchase #6 $247.76   5.598%   $261.6296   $261.63   $261.65   $261.60  
  Purchase #7 $180.95   5.561%   $191.0126   $191.01   $191.00   $191.00  
  7 purchase totals = $1,241.86       $1,352.2483   $1,352.24   $1,352.25   $1,352.20