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 $208.74   8.536%   $226.558   $226.56   $226.55   $226.60  
  Purchase #2 $162.29   9.197%   $177.2158   $177.22   $177.20   $177.20  
  Purchase #3 $32.53   11.577%   $36.296   $36.30   $36.30   $36.30  
  Purchase #4 $212.77   7.369%   $228.449   $228.45   $228.45   $228.40  
  Purchase #5 $90.92   4.128%   $94.6732   $94.67   $94.65   $94.70  
  Purchase #6 $25.90   11.249%   $28.8135   $28.81   $28.80   $28.80  
  Purchase #7 $58.37   9.733%   $64.0512   $64.05   $64.05   $64.10  
  7 purchase totals = $791.52       $856.0567   $856.06   $856.00   $856.10