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 $231.95   11.228%   $257.9933   $257.99   $258.00   $258.00  
  Purchase #2 $54.51   6.861%   $58.2499   $58.25   $58.25   $58.20  
  Purchase #3 $58.90   7.490%   $63.3116   $63.31   $63.30   $63.30  
  Purchase #4 $192.71   7.193%   $206.5716   $206.57   $206.55   $206.60  
  Purchase #5 $189.26   11.503%   $211.0306   $211.03   $211.05   $211.00  
  Purchase #6 $47.45   7.466%   $50.9926   $50.99   $51.00   $51.00  
  Purchase #7 $163.78   11.126%   $182.0022   $182.00   $182.00   $182.00  
  7 purchase totals = $938.56       $1,030.1518   $1,030.14   $1,030.15   $1,030.10