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 $132.67   6.694%   $141.5509   $141.55   $141.55   $141.60  
  Purchase #2 $182.25   5.574%   $192.4086   $192.41   $192.40   $192.40  
  Purchase #3 $198.59   8.352%   $215.1762   $215.18   $215.20   $215.20  
  Purchase #4 $194.71   10.775%   $215.69   $215.69   $215.70   $215.70  
  Purchase #5 $127.32   8.642%   $138.323   $138.32   $138.30   $138.30  
  Purchase #6 $103.87   10.619%   $114.9   $114.90   $114.90   $114.90  
  Purchase #7 $91.77   13.552%   $104.2067   $104.21   $104.20   $104.20  
  7 purchase totals = $1,031.18       $1,122.2554   $1,122.26   $1,122.25   $1,122.30