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 $226.75   4.194%   $236.2599   $236.26   $236.25   $236.30  
  Purchase #2 $146.88   10.156%   $161.7971   $161.80   $161.80   $161.80  
  Purchase #3 $148.32   10.307%   $163.6073   $163.61   $163.60   $163.60  
  Purchase #4 $167.87   5.605%   $177.2791   $177.28   $177.30   $177.30  
  Purchase #5 $118.68   8.356%   $128.5969   $128.60   $128.60   $128.60  
  Purchase #6 $32.87   12.299%   $36.9127   $36.91   $36.90   $36.90  
  Purchase #7 $145.76   8.557%   $158.2327   $158.23   $158.25   $158.20  
  7 purchase totals = $987.13       $1,062.6857   $1,062.69   $1,062.70   $1,062.70