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 $222.53   4.379%   $232.2746   $232.27   $232.25   $232.30  
  Purchase #2 $230.34   9.582%   $252.4112   $252.41   $252.40   $252.40  
  Purchase #3 $196.67   10.759%   $217.8297   $217.83   $217.85   $217.80  
  Purchase #4 $98.46   7.599%   $105.942   $105.94   $105.95   $105.90  
  Purchase #5 $162.72   12.654%   $183.3106   $183.31   $183.30   $183.30  
  Purchase #6 $236.28   7.629%   $254.3058   $254.31   $254.30   $254.30  
  Purchase #7 $110.74   3.367%   $114.4686   $114.47   $114.45   $114.50  
  7 purchase totals = $1,257.74       $1,360.5425   $1,360.54   $1,360.50   $1,360.50