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 $119.86   12.504%   $134.8473   $134.85   $134.85   $134.80  
  Purchase #2 $208.61   3.161%   $215.2042   $215.20   $215.20   $215.20  
  Purchase #3 $66.43   11.509%   $74.0754   $74.08   $74.10   $74.10  
  Purchase #4 $187.80   4.591%   $196.4219   $196.42   $196.40   $196.40  
  Purchase #5 $117.50   10.162%   $129.4404   $129.44   $129.45   $129.40  
  Purchase #6 $246.28   5.373%   $259.5126   $259.51   $259.50   $259.50  
  Purchase #7 $91.90   6.751%   $98.1042   $98.10   $98.10   $98.10  
  7 purchase totals = $1,038.38       $1,107.6060   $1,107.60   $1,107.60   $1,107.50