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 $181.62   11.283%   $202.1122   $202.11   $202.10   $202.10  
  Purchase #2 $89.44   13.641%   $101.6405   $101.64   $101.65   $101.60  
  Purchase #3 $97.49   10.766%   $107.9858   $107.99   $108.00   $108.00  
  Purchase #4 $109.83   5.676%   $116.064   $116.06   $116.05   $116.10  
  Purchase #5 $24.97   12.137%   $28.0006   $28.00   $28.00   $28.00  
  Purchase #6 $7.94   3.638%   $8.2289   $8.23   $8.25   $8.20  
  Purchase #7 $104.79   7.836%   $113.0013   $113.00   $113.00   $113.00  
  7 purchase totals = $616.08       $677.0333   $677.03   $677.05   $677.00