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 $229.60   13.329%   $260.2034   $260.20   $260.20   $260.20  
  Purchase #2 $97.94   6.728%   $104.5294   $104.53   $104.55   $104.50  
  Purchase #3 $28.93   13.111%   $32.723   $32.72   $32.70   $32.70  
  Purchase #4 $163.28   8.774%   $177.6062   $177.61   $177.60   $177.60  
  Purchase #5 $202.84   10.643%   $224.4283   $224.43   $224.45   $224.40  
  Purchase #6 $73.36   6.211%   $77.9164   $77.92   $77.90   $77.90  
  Purchase #7 $226.70   13.188%   $256.5972   $256.60   $256.60   $256.60  
  7 purchase totals = $1,022.65       $1,134.0039   $1,134.01   $1,134.00   $1,133.90