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 $248.31   8.620%   $269.7143   $269.71   $269.70   $269.70  
  Purchase #2 $249.82   4.853%   $261.9438   $261.94   $261.95   $261.90  
  Purchase #3 $178.76   3.108%   $184.3159   $184.32   $184.30   $184.30  
  Purchase #4 $160.29   10.182%   $176.6107   $176.61   $176.60   $176.60  
  Purchase #5 $23.56   4.594%   $24.6423   $24.64   $24.65   $24.60  
  Purchase #6 $22.84   5.356%   $24.0633   $24.06   $24.05   $24.10  
  Purchase #7 $161.75   13.171%   $183.0541   $183.05   $183.05   $183.10  
  7 purchase totals = $1,045.33       $1,124.3444   $1,124.33   $1,124.30   $1,124.30