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 $238.77   4.139%   $248.6527   $248.65   $248.65   $248.70  
  Purchase #2 $199.96   8.232%   $216.4207   $216.42   $216.40   $216.40  
  Purchase #3 $57.30   11.192%   $63.713   $63.71   $63.70   $63.70  
  Purchase #4 $58.99   7.150%   $63.2078   $63.21   $63.20   $63.20  
  Purchase #5 $52.45   9.179%   $57.2644   $57.26   $57.25   $57.30  
  Purchase #6 $183.59   7.189%   $196.7883   $196.79   $196.80   $196.80  
  Purchase #7 $190.74   5.839%   $201.8773   $201.88   $201.90   $201.90  
  7 purchase totals = $981.80       $1,047.9242   $1,047.92   $1,047.90   $1,048.00