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 $58.48   7.773%   $63.0257   $63.03   $63.05   $63.00  
  Purchase #2 $93.47   13.566%   $106.1501   $106.15   $106.15   $106.20  
  Purchase #3 $201.79   3.377%   $208.6044   $208.60   $208.60   $208.60  
  Purchase #4 $115.72   10.812%   $128.2316   $128.23   $128.25   $128.20  
  Purchase #5 $24.90   7.669%   $26.8096   $26.81   $26.80   $26.80  
  Purchase #6 $94.68   10.605%   $104.7208   $104.72   $104.70   $104.70  
  Purchase #7 $26.60   11.724%   $29.7186   $29.72   $29.70   $29.70  
  7 purchase totals = $615.64       $667.2608   $667.26   $667.25   $667.20