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 $38.26   6.539%   $40.7618   $40.76   $40.75   $40.80  
  Purchase #2 $231.54   10.102%   $254.9302   $254.93   $254.95   $254.90  
  Purchase #3 $208.83   12.306%   $234.5286   $234.53   $234.55   $234.50  
  Purchase #4 $180.94   10.260%   $199.5044   $199.50   $199.50   $199.50  
  Purchase #5 $129.61   13.419%   $147.0024   $147.00   $147.00   $147.00  
  Purchase #6 $27.30   13.334%   $30.9402   $30.94   $30.95   $30.90  
  Purchase #7 $177.79   10.229%   $195.9761   $195.98   $196.00   $196.00  
  7 purchase totals = $994.27       $1,103.6437   $1,103.64   $1,103.70   $1,103.60