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 $216.83   13.517%   $246.1389   $246.14   $246.15   $246.10  
  Purchase #2 $76.81   8.338%   $83.2144   $83.21   $83.20   $83.20  
  Purchase #3 $26.37   3.673%   $27.3386   $27.34   $27.35   $27.30  
  Purchase #4 $245.86   11.668%   $274.5469   $274.55   $274.55   $274.50  
  Purchase #5 $68.88   12.670%   $77.6071   $77.61   $77.60   $77.60  
  Purchase #6 $213.44   3.786%   $221.5208   $221.52   $221.50   $221.50  
  Purchase #7 $101.76   10.842%   $112.7928   $112.79   $112.80   $112.80  
  7 purchase totals = $949.95       $1,043.1595   $1,043.16   $1,043.15   $1,043.00