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 $58.74   7.737%   $63.2847   $63.28   $63.30   $63.30  
  Purchase #2 $181.96   11.105%   $202.1667   $202.17   $202.15   $202.20  
  Purchase #3 $181.43   8.396%   $196.6629   $196.66   $196.65   $196.70  
  Purchase #4 $208.83   13.354%   $236.7172   $236.72   $236.70   $236.70  
  Purchase #5 $89.58   7.374%   $96.1856   $96.19   $96.20   $96.20  
  Purchase #6 $242.59   9.228%   $264.9762   $264.98   $265.00   $265.00  
  Purchase #7 $193.69   4.702%   $202.7973   $202.80   $202.80   $202.80  
  7 purchase totals = $1,156.82       $1,262.7906   $1,262.80   $1,262.80   $1,262.90