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 $105.62   12.614%   $118.9429   $118.94   $118.95   $118.90  
  Purchase #2 $11.48   4.543%   $12.0015   $12.00   $12.00   $12.00  
  Purchase #3 $248.83   5.354%   $262.1524   $262.15   $262.15   $262.20  
  Purchase #4 $188.73   12.223%   $211.7985   $211.80   $211.80   $211.80  
  Purchase #5 $240.28   9.286%   $262.5924   $262.59   $262.60   $262.60  
  Purchase #6 $38.65   3.217%   $39.8934   $39.89   $39.90   $39.90  
  Purchase #7 $107.68   10.191%   $118.6537   $118.65   $118.65   $118.70  
  7 purchase totals = $941.27       $1,026.0348   $1,026.02   $1,026.05   $1,026.10