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 $220.75   3.469%   $228.4078   $228.41   $228.40   $228.40  
  Purchase #2 $137.88   11.284%   $153.4384   $153.44   $153.45   $153.40  
  Purchase #3 $37.91   8.866%   $41.2711   $41.27   $41.25   $41.30  
  Purchase #4 $249.65   11.357%   $278.0028   $278.00   $278.00   $278.00  
  Purchase #5 $33.61   7.500%   $36.1308   $36.13   $36.15   $36.10  
  Purchase #6 $96.97   11.553%   $108.1729   $108.17   $108.15   $108.20  
  Purchase #7 $163.73   11.853%   $183.1369   $183.14   $183.15   $183.10  
  7 purchase totals = $940.50       $1,028.5607   $1,028.56   $1,028.55   $1,028.50