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 $250.25   7.617%   $269.3115   $269.31   $269.30   $269.30  
  Purchase #2 $107.57   9.523%   $117.8139   $117.81   $117.80   $117.80  
  Purchase #3 $10.99   4.444%   $11.4784   $11.48   $11.50   $11.50  
  Purchase #4 $102.40   3.424%   $105.9062   $105.91   $105.90   $105.90  
  Purchase #5 $185.73   3.253%   $191.7718   $191.77   $191.75   $191.80  
  Purchase #6 $178.77   3.318%   $184.7016   $184.70   $184.70   $184.70  
  Purchase #7 $157.57   5.644%   $166.4633   $166.46   $166.45   $166.50  
  7 purchase totals = $993.28       $1,047.4467   $1,047.44   $1,047.40   $1,047.50