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 $241.28   11.480%   $268.9789   $268.98   $269.00   $269.00  
  Purchase #2 $57.51   9.538%   $62.9953   $63.00   $63.00   $63.00  
  Purchase #3 $97.56   10.334%   $107.6419   $107.64   $107.65   $107.60  
  Purchase #4 $54.63   3.167%   $56.3601   $56.36   $56.35   $56.40  
  Purchase #5 $29.53   12.741%   $33.2924   $33.29   $33.30   $33.30  
  Purchase #6 $206.85   13.138%   $234.026   $234.03   $234.05   $234.00  
  Purchase #7 $211.66   9.324%   $231.3952   $231.40   $231.40   $231.40  
  7 purchase totals = $899.02       $994.6898   $994.70   $994.75   $994.70