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 $58.94   11.195%   $65.5383   $65.54   $65.55   $65.50  
  Purchase #2 $130.96   9.234%   $143.0528   $143.05   $143.05   $143.10  
  Purchase #3 $192.32   12.763%   $216.8658   $216.87   $216.85   $216.90  
  Purchase #4 $186.99   6.193%   $198.5703   $198.57   $198.55   $198.60  
  Purchase #5 $53.65   7.802%   $57.8358   $57.84   $57.85   $57.80  
  Purchase #6 $163.66   4.792%   $171.5026   $171.50   $171.50   $171.50  
  Purchase #7 $7.63   7.285%   $8.1858   $8.19   $8.20   $8.20  
  7 purchase totals = $794.15       $861.5514   $861.56   $861.55   $861.60