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 $192.58   13.302%   $218.197   $218.20   $218.20   $218.20  
  Purchase #2 $201.32   3.491%   $208.3481   $208.35   $208.35   $208.30  
  Purchase #3 $146.42   5.152%   $153.9636   $153.96   $153.95   $154.00  
  Purchase #4 $185.87   6.463%   $197.8828   $197.88   $197.90   $197.90  
  Purchase #5 $57.87   6.202%   $61.4591   $61.46   $61.45   $61.50  
  Purchase #6 $29.77   7.522%   $32.0093   $32.01   $32.00   $32.00  
  Purchase #7 $177.89   8.636%   $193.2526   $193.25   $193.25   $193.30  
  7 purchase totals = $991.72       $1,065.1125   $1,065.11   $1,065.10   $1,065.20