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 $226.47   6.754%   $241.7658   $241.77   $241.75   $241.80  
  Purchase #2 $179.29   9.495%   $196.3136   $196.31   $196.30   $196.30  
  Purchase #3 $193.32   7.536%   $207.8886   $207.89   $207.90   $207.90  
  Purchase #4 $151.48   13.855%   $172.4676   $172.47   $172.45   $172.50  
  Purchase #5 $49.54   4.113%   $51.5776   $51.58   $51.60   $51.60  
  Purchase #6 $145.26   7.246%   $155.7855   $155.79   $155.80   $155.80  
  Purchase #7 $169.87   9.773%   $186.4714   $186.47   $186.45   $186.50  
  7 purchase totals = $1,115.23       $1,212.2701   $1,212.28   $1,212.25   $1,212.40