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 $58.92   13.645%   $66.9596   $66.96   $66.95   $67.00  
  Purchase #2 $240.93   8.724%   $261.9487   $261.95   $261.95   $261.90  
  Purchase #3 $158.56   11.527%   $176.8372   $176.84   $176.85   $176.80  
  Purchase #4 $114.82   4.719%   $120.2384   $120.24   $120.25   $120.20  
  Purchase #5 $61.77   8.620%   $67.0946   $67.09   $67.10   $67.10  
  Purchase #6 $115.51   4.623%   $120.85   $120.85   $120.85   $120.90  
  Purchase #7 $124.97   5.116%   $131.3635   $131.36   $131.35   $131.40  
  7 purchase totals = $875.48       $945.2920   $945.29   $945.30   $945.30