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 $92.69   8.157%   $100.2507   $100.25   $100.25   $100.30  
  Purchase #2 $222.68   10.671%   $246.4422   $246.44   $246.45   $246.40  
  Purchase #3 $234.61   11.284%   $261.0834   $261.08   $261.10   $261.10  
  Purchase #4 $216.28   4.229%   $225.4265   $225.43   $225.45   $225.40  
  Purchase #5 $231.25   9.198%   $252.5204   $252.52   $252.50   $252.50  
  Purchase #6 $186.93   11.574%   $208.5653   $208.57   $208.55   $208.60  
  Purchase #7 $175.73   11.530%   $195.9917   $195.99   $196.00   $196.00  
  7 purchase totals = $1,360.17       $1,490.2802   $1,490.28   $1,490.30   $1,490.30