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 $58.56   11.602%   $65.3541   $65.35   $65.35   $65.40  
  Purchase #2 $114.55   4.571%   $119.7861   $119.79   $119.80   $119.80  
  Purchase #3 $49.26   10.509%   $54.4367   $54.44   $54.45   $54.40  
  Purchase #4 $200.88   8.591%   $218.1376   $218.14   $218.15   $218.10  
  Purchase #5 $246.63   6.588%   $262.878   $262.88   $262.90   $262.90  
  Purchase #6 $30.60   13.134%   $34.619   $34.62   $34.60   $34.60  
  Purchase #7 $79.51   10.821%   $88.1138   $88.11   $88.10   $88.10  
  7 purchase totals = $779.99       $843.3253   $843.33   $843.35   $843.30