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 $208.86   13.225%   $236.4817   $236.48   $236.50   $236.50  
  Purchase #2 $211.91   11.348%   $235.9575   $235.96   $235.95   $236.00  
  Purchase #3 $63.84   12.218%   $71.64   $71.64   $71.65   $71.60  
  Purchase #4 $240.92   12.193%   $270.2954   $270.30   $270.30   $270.30  
  Purchase #5 $58.95   3.376%   $60.9402   $60.94   $60.95   $60.90  
  Purchase #6 $187.76   9.397%   $205.4038   $205.40   $205.40   $205.40  
  Purchase #7 $228.34   5.421%   $240.7183   $240.72   $240.70   $240.70  
  7 purchase totals = $1,200.58       $1,321.4369   $1,321.44   $1,321.45   $1,321.40