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 $82.74   5.327%   $87.1476   $87.15   $87.15   $87.10  
  Purchase #2 $44.55   4.502%   $46.5556   $46.56   $46.55   $46.60  
  Purchase #3 $114.71   7.160%   $122.9232   $122.92   $122.90   $122.90  
  Purchase #4 $196.91   4.755%   $206.2731   $206.27   $206.25   $206.30  
  Purchase #5 $204.77   13.624%   $232.6679   $232.67   $232.65   $232.70  
  Purchase #6 $241.49   12.633%   $271.9974   $272.00   $272.00   $272.00  
  Purchase #7 $98.46   8.839%   $107.1629   $107.16   $107.15   $107.20  
  7 purchase totals = $983.63       $1,074.7277   $1,074.73   $1,074.65   $1,074.80