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 $24.85   8.602%   $26.9876   $26.99   $27.00   $27.00  
  Purchase #2 $208.72   3.392%   $215.7998   $215.80   $215.80   $215.80  
  Purchase #3 $89.39   5.771%   $94.5487   $94.55   $94.55   $94.50  
  Purchase #4 $241.62   8.518%   $262.2012   $262.20   $262.20   $262.20  
  Purchase #5 $22.66   5.873%   $23.9908   $23.99   $24.00   $24.00  
  Purchase #6 $242.30   8.297%   $262.4036   $262.40   $262.40   $262.40  
  Purchase #7 $180.93   13.856%   $205.9997   $206.00   $206.00   $206.00  
  7 purchase totals = $1,010.47       $1,091.9314   $1,091.93   $1,091.95   $1,091.90