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 $236.43   10.374%   $260.9572   $260.96   $260.95   $261.00  
  Purchase #2 $186.77   8.718%   $203.0526   $203.05   $203.05   $203.10  
  Purchase #3 $163.26   8.318%   $176.84   $176.84   $176.85   $176.80  
  Purchase #4 $178.80   11.140%   $198.7183   $198.72   $198.70   $198.70  
  Purchase #5 $153.81   13.357%   $174.3544   $174.35   $174.35   $174.40  
  Purchase #6 $72.93   6.598%   $77.7419   $77.74   $77.75   $77.70  
  Purchase #7 $71.77   6.360%   $76.3346   $76.33   $76.35   $76.30  
  7 purchase totals = $1,063.77       $1,167.9990   $1,167.99   $1,168.00   $1,168.00