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 $76.78   12.591%   $86.4474   $86.45   $86.45   $86.40  
  Purchase #2 $215.86   6.537%   $229.9708   $229.97   $229.95   $230.00  
  Purchase #3 $175.77   11.325%   $195.676   $195.68   $195.70   $195.70  
  Purchase #4 $105.31   12.148%   $118.1031   $118.10   $118.10   $118.10  
  Purchase #5 $38.94   9.136%   $42.4976   $42.50   $42.50   $42.50  
  Purchase #6 $215.76   5.607%   $227.8577   $227.86   $227.85   $227.90  
  Purchase #7 $133.63   10.542%   $147.7173   $147.72   $147.70   $147.70  
  7 purchase totals = $962.05       $1,048.2699   $1,048.28   $1,048.25   $1,048.30