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 $156.61   12.491%   $176.1722   $176.17   $176.15   $176.20  
  Purchase #2 $178.71   9.115%   $194.9994   $195.00   $195.00   $195.00  
  Purchase #3 $126.38   5.742%   $133.6367   $133.64   $133.65   $133.60  
  Purchase #4 $117.60   4.126%   $122.4522   $122.45   $122.45   $122.50  
  Purchase #5 $219.77   3.801%   $228.1235   $228.12   $228.10   $228.10  
  Purchase #6 $98.76   7.873%   $106.5354   $106.54   $106.55   $106.50  
  Purchase #7 $59.92   10.198%   $66.0306   $66.03   $66.05   $66.00  
  7 purchase totals = $957.75       $1,027.9500   $1,027.95   $1,027.95   $1,027.90