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 $232.84   3.752%   $241.5762   $241.58   $241.60   $241.60  
  Purchase #2 $32.81   10.473%   $36.2462   $36.25   $36.25   $36.20  
  Purchase #3 $182.83   7.375%   $196.3137   $196.31   $196.30   $196.30  
  Purchase #4 $53.50   9.279%   $58.4643   $58.46   $58.45   $58.50  
  Purchase #5 $249.56   11.421%   $278.0622   $278.06   $278.05   $278.10  
  Purchase #6 $164.60   7.268%   $176.5631   $176.56   $176.55   $176.60  
  Purchase #7 $12.99   8.439%   $14.0862   $14.09   $14.10   $14.10  
  7 purchase totals = $929.13       $1,001.3119   $1,001.31   $1,001.30   $1,001.40