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 $169.49   9.461%   $185.5254   $185.53   $185.55   $185.50  
  Purchase #2 $197.28   4.239%   $205.6427   $205.64   $205.65   $205.60  
  Purchase #3 $179.99   12.629%   $202.7209   $202.72   $202.70   $202.70  
  Purchase #4 $85.68   4.437%   $89.4816   $89.48   $89.50   $89.50  
  Purchase #5 $243.96   7.290%   $261.7447   $261.74   $261.75   $261.70  
  Purchase #6 $156.61   4.226%   $163.2283   $163.23   $163.25   $163.20  
  Purchase #7 $221.89   6.483%   $236.2751   $236.28   $236.30   $236.30  
  7 purchase totals = $1,254.90       $1,344.6187   $1,344.62   $1,344.70   $1,344.50