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 $226.96   11.458%   $252.9651   $252.97   $252.95   $253.00  
  Purchase #2 $33.51   10.400%   $36.995   $37.00   $37.00   $37.00  
  Purchase #3 $180.70   8.459%   $195.9854   $195.99   $196.00   $196.00  
  Purchase #4 $6.69   5.619%   $7.0659   $7.07   $7.05   $7.10  
  Purchase #5 $234.52   11.462%   $261.4007   $261.40   $261.40   $261.40  
  Purchase #6 $18.41   4.587%   $19.2545   $19.25   $19.25   $19.30  
  Purchase #7 $210.54   5.141%   $221.3639   $221.36   $221.35   $221.40  
  7 purchase totals = $911.33       $995.0305   $995.04   $995.00   $995.20