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 $229.82   11.562%   $256.3918   $256.39   $256.40   $256.40  
  Purchase #2 $217.81   4.359%   $227.3043   $227.30   $227.30   $227.30  
  Purchase #3 $56.80   6.821%   $60.6743   $60.67   $60.65   $60.70  
  Purchase #4 $67.91   5.737%   $71.806   $71.81   $71.80   $71.80  
  Purchase #5 $135.54   10.368%   $149.5928   $149.59   $149.60   $149.60  
  Purchase #6 $250.91   4.576%   $262.3916   $262.39   $262.40   $262.40  
  Purchase #7 $224.67   4.653%   $235.1239   $235.12   $235.10   $235.10  
  7 purchase totals = $1,183.46       $1,263.2847   $1,263.27   $1,263.25   $1,263.30