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 $61.74   6.280%   $65.6173   $65.62   $65.60   $65.60  
  Purchase #2 $192.56   3.631%   $199.5519   $199.55   $199.55   $199.60  
  Purchase #3 $106.29   4.694%   $111.2793   $111.28   $111.30   $111.30  
  Purchase #4 $106.32   8.423%   $115.2753   $115.28   $115.30   $115.30  
  Purchase #5 $215.60   10.180%   $237.5481   $237.55   $237.55   $237.50  
  Purchase #6 $228.99   9.212%   $250.0846   $250.08   $250.10   $250.10  
  Purchase #7 $183.26   5.570%   $193.4676   $193.47   $193.45   $193.50  
  7 purchase totals = $1,094.76       $1,172.8241   $1,172.83   $1,172.85   $1,172.90