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 $29.94   8.159%   $32.3828   $32.38   $32.40   $32.40  
  Purchase #2 $230.48   7.754%   $248.3514   $248.35   $248.35   $248.40  
  Purchase #3 $144.47   4.125%   $150.4294   $150.43   $150.45   $150.40  
  Purchase #4 $169.76   5.607%   $179.2784   $179.28   $179.30   $179.30  
  Purchase #5 $249.26   9.795%   $273.675   $273.68   $273.70   $273.70  
  Purchase #6 $181.38   13.254%   $205.4201   $205.42   $205.40   $205.40  
  Purchase #7 $106.35   9.652%   $116.6149   $116.61   $116.60   $116.60  
  7 purchase totals = $1,111.64       $1,206.1520   $1,206.15   $1,206.20   $1,206.20