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 $97.57   6.764%   $104.1696   $104.17   $104.15   $104.20  
  Purchase #2 $236.26   11.365%   $263.1109   $263.11   $263.10   $263.10  
  Purchase #3 $129.77   9.553%   $142.1669   $142.17   $142.15   $142.20  
  Purchase #4 $200.57   3.202%   $206.9923   $206.99   $207.00   $207.00  
  Purchase #5 $164.25   7.873%   $177.1814   $177.18   $177.20   $177.20  
  Purchase #6 $49.95   12.403%   $56.1453   $56.15   $56.15   $56.10  
  Purchase #7 $139.86   4.484%   $146.1313   $146.13   $146.15   $146.10  
  7 purchase totals = $1,018.23       $1,095.8977   $1,095.90   $1,095.90   $1,095.90