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 $114.92   11.113%   $127.6911   $127.69   $127.70   $127.70  
  Purchase #2 $114.72   4.396%   $119.7631   $119.76   $119.75   $119.80  
  Purchase #3 $249.56   10.806%   $276.5275   $276.53   $276.55   $276.50  
  Purchase #4 $188.84   4.167%   $196.709   $196.71   $196.70   $196.70  
  Purchase #5 $217.67   5.790%   $230.2731   $230.27   $230.25   $230.30  
  Purchase #6 $164.80   10.146%   $181.5206   $181.52   $181.50   $181.50  
  Purchase #7 $106.50   7.690%   $114.6899   $114.69   $114.70   $114.70  
  7 purchase totals = $1,157.01       $1,247.1743   $1,247.17   $1,247.15   $1,247.20