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 $152.68   10.206%   $168.2625   $168.26   $168.25   $168.30  
  Purchase #2 $61.47   5.388%   $64.782   $64.78   $64.80   $64.80  
  Purchase #3 $226.72   5.424%   $239.0173   $239.02   $239.00   $239.00  
  Purchase #4 $161.58   6.733%   $172.4592   $172.46   $172.45   $172.50  
  Purchase #5 $196.41   4.446%   $205.1424   $205.14   $205.15   $205.10  
  Purchase #6 $163.69   12.274%   $183.7813   $183.78   $183.80   $183.80  
  Purchase #7 $78.50   4.137%   $81.7475   $81.75   $81.75   $81.70  
  7 purchase totals = $1,041.05       $1,115.1922   $1,115.19   $1,115.20   $1,115.20