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 $127.95   5.504%   $134.9924   $134.99   $135.00   $135.00  
  Purchase #2 $232.60   6.693%   $248.1679   $248.17   $248.15   $248.20  
  Purchase #3 $167.51   5.229%   $176.2691   $176.27   $176.25   $176.30  
  Purchase #4 $34.96   7.383%   $37.5411   $37.54   $37.55   $37.50  
  Purchase #5 $231.50   10.115%   $254.9162   $254.92   $254.90   $254.90  
  Purchase #6 $59.61   9.531%   $65.2914   $65.29   $65.30   $65.30  
  Purchase #7 $107.83   11.174%   $119.8789   $119.88   $119.90   $119.90  
  7 purchase totals = $961.96       $1,037.0570   $1,037.06   $1,037.05   $1,037.10