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 $53.81   5.194%   $56.6049   $56.60   $56.60   $56.60  
  Purchase #2 $123.33   4.661%   $129.0784   $129.08   $129.10   $129.10  
  Purchase #3 $92.90   6.237%   $98.6942   $98.69   $98.70   $98.70  
  Purchase #4 $227.69   13.531%   $258.4987   $258.50   $258.50   $258.50  
  Purchase #5 $185.50   12.228%   $208.1829   $208.18   $208.20   $208.20  
  Purchase #6 $122.92   5.626%   $129.8355   $129.84   $129.85   $129.80  
  Purchase #7 $142.89   9.418%   $156.3474   $156.35   $156.35   $156.30  
  7 purchase totals = $949.04       $1,037.2420   $1,037.24   $1,037.30   $1,037.20