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 $227.46   12.568%   $256.0472   $256.05   $256.05   $256.00  
  Purchase #2 $208.44   6.109%   $221.1736   $221.17   $221.15   $221.20  
  Purchase #3 $75.32   3.271%   $77.7837   $77.78   $77.80   $77.80  
  Purchase #4 $235.84   5.467%   $248.7334   $248.73   $248.75   $248.70  
  Purchase #5 $194.36   4.182%   $202.4881   $202.49   $202.50   $202.50  
  Purchase #6 $130.46   3.640%   $135.2087   $135.21   $135.20   $135.20  
  Purchase #7 $188.93   6.182%   $200.6097   $200.61   $200.60   $200.60  
  7 purchase totals = $1,260.81       $1,342.0444   $1,342.04   $1,342.05   $1,342.00