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 $65.51   4.243%   $68.2896   $68.29   $68.30   $68.30  
  Purchase #2 $10.79   3.302%   $11.1463   $11.15   $11.15   $11.10  
  Purchase #3 $246.28   4.120%   $256.4267   $256.43   $256.45   $256.40  
  Purchase #4 $86.81   6.779%   $92.6948   $92.69   $92.70   $92.70  
  Purchase #5 $67.44   11.852%   $75.433   $75.43   $75.45   $75.40  
  Purchase #6 $73.48   5.196%   $77.298   $77.30   $77.30   $77.30  
  Purchase #7 $126.81   11.436%   $141.312   $141.31   $141.30   $141.30  
  7 purchase totals = $677.12       $722.6004   $722.60   $722.65   $722.50