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 $196.74   6.194%   $208.9261   $208.93   $208.95   $208.90  
  Purchase #2 $116.92   12.536%   $131.5771   $131.58   $131.60   $131.60  
  Purchase #3 $54.75   5.804%   $57.9277   $57.93   $57.95   $57.90  
  Purchase #4 $170.32   3.424%   $176.1518   $176.15   $176.15   $176.20  
  Purchase #5 $111.96   6.690%   $119.4501   $119.45   $119.45   $119.50  
  Purchase #6 $176.48   12.361%   $198.2947   $198.29   $198.30   $198.30  
  Purchase #7 $119.50   12.720%   $134.7004   $134.70   $134.70   $134.70  
  7 purchase totals = $946.67       $1,027.0279   $1,027.03   $1,027.10   $1,027.10