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 $204.85   6.537%   $218.241   $218.24   $218.25   $218.20  
  Purchase #2 $165.76   10.590%   $183.314   $183.31   $183.30   $183.30  
  Purchase #3 $16.30   11.500%   $18.1745   $18.17   $18.15   $18.20  
  Purchase #4 $47.32   13.320%   $53.623   $53.62   $53.60   $53.60  
  Purchase #5 $207.33   8.172%   $224.273   $224.27   $224.25   $224.30  
  Purchase #6 $63.27   3.188%   $65.287   $65.29   $65.30   $65.30  
  Purchase #7 $185.42   8.461%   $201.1084   $201.11   $201.10   $201.10  
  7 purchase totals = $890.25       $964.0209   $964.01   $963.95   $964.00