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 $242.66   8.362%   $262.9512   $262.95   $262.95   $263.00  
  Purchase #2 $51.95   12.301%   $58.3404   $58.34   $58.35   $58.30  
  Purchase #3 $136.25   4.632%   $142.5611   $142.56   $142.55   $142.60  
  Purchase #4 $24.85   4.791%   $26.0406   $26.04   $26.05   $26.00  
  Purchase #5 $10.65   3.539%   $11.0269   $11.03   $11.05   $11.00  
  Purchase #6 $242.98   10.749%   $269.0979   $269.10   $269.10   $269.10  
  Purchase #7 $37.41   4.450%   $39.0747   $39.07   $39.05   $39.10  
  7 purchase totals = $746.75       $809.0928   $809.09   $809.10   $809.10