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 $238.69   3.193%   $246.3114   $246.31   $246.30   $246.30  
  Purchase #2 $55.78   7.626%   $60.0338   $60.03   $60.05   $60.00  
  Purchase #3 $21.55   6.616%   $22.9757   $22.98   $23.00   $23.00  
  Purchase #4 $125.32   5.499%   $132.2113   $132.21   $132.20   $132.20  
  Purchase #5 $230.47   4.655%   $241.1984   $241.20   $241.20   $241.20  
  Purchase #6 $75.66   3.703%   $78.4617   $78.46   $78.45   $78.50  
  Purchase #7 $166.25   5.548%   $175.4736   $175.47   $175.45   $175.50  
  7 purchase totals = $913.72       $956.6659   $956.66   $956.65   $956.70