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 $213.26   13.640%   $242.3487   $242.35   $242.35   $242.30  
  Purchase #2 $67.59   7.561%   $72.7005   $72.70   $72.70   $72.70  
  Purchase #3 $226.51   9.668%   $248.409   $248.41   $248.40   $248.40  
  Purchase #4 $183.58   12.132%   $205.8519   $205.85   $205.85   $205.90  
  Purchase #5 $121.89   9.211%   $133.1173   $133.12   $133.10   $133.10  
  Purchase #6 $248.71   8.136%   $268.945   $268.95   $268.95   $268.90  
  Purchase #7 $95.61   7.242%   $102.5341   $102.53   $102.55   $102.50  
  7 purchase totals = $1,157.15       $1,273.9065   $1,273.91   $1,273.90   $1,273.80