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 $237.52   10.212%   $261.7755   $261.78   $261.80   $261.80  
  Purchase #2 $172.25   7.862%   $185.7923   $185.79   $185.80   $185.80  
  Purchase #3 $193.89   8.248%   $209.882   $209.88   $209.90   $209.90  
  Purchase #4 $54.32   10.575%   $60.0643   $60.06   $60.05   $60.10  
  Purchase #5 $248.28   11.761%   $277.4802   $277.48   $277.50   $277.50  
  Purchase #6 $56.44   13.182%   $63.8799   $63.88   $63.90   $63.90  
  Purchase #7 $162.62   12.415%   $182.8093   $182.81   $182.80   $182.80  
  7 purchase totals = $1,125.32       $1,241.6835   $1,241.68   $1,241.75   $1,241.80