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 $236.73   11.591%   $264.1694   $264.17   $264.15   $264.20  
  Purchase #2 $212.82   3.558%   $220.3921   $220.39   $220.40   $220.40  
  Purchase #3 $200.86   10.726%   $222.4042   $222.40   $222.40   $222.40  
  Purchase #4 $154.45   8.493%   $167.5674   $167.57   $167.55   $167.60  
  Purchase #5 $169.62   4.559%   $177.353   $177.35   $177.35   $177.40  
  Purchase #6 $234.90   10.394%   $259.3155   $259.32   $259.30   $259.30  
  Purchase #7 $45.28   10.633%   $50.0946   $50.09   $50.10   $50.10  
  7 purchase totals = $1,254.66       $1,361.2962   $1,361.29   $1,361.25   $1,361.40