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 $237.35   9.413%   $259.6918   $259.69   $259.70   $259.70  
  Purchase #2 $75.66   10.149%   $83.3387   $83.34   $83.35   $83.30  
  Purchase #3 $206.35   3.555%   $213.6857   $213.69   $213.70   $213.70  
  Purchase #4 $87.76   3.184%   $90.5543   $90.55   $90.55   $90.60  
  Purchase #5 $154.67   13.168%   $175.0369   $175.04   $175.05   $175.00  
  Purchase #6 $101.44   5.522%   $107.0415   $107.04   $107.05   $107.00  
  Purchase #7 $107.82   13.834%   $122.7358   $122.74   $122.75   $122.70  
  7 purchase totals = $971.05       $1,052.0847   $1,052.09   $1,052.15   $1,052.00