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 $84.77   11.526%   $94.5406   $94.54   $94.55   $94.50  
  Purchase #2 $13.95   13.814%   $15.8771   $15.88   $15.90   $15.90  
  Purchase #3 $208.83   9.285%   $228.2199   $228.22   $228.20   $228.20  
  Purchase #4 $169.57   10.620%   $187.5783   $187.58   $187.60   $187.60  
  Purchase #5 $32.81   6.833%   $35.0519   $35.05   $35.05   $35.10  
  Purchase #6 $200.38   10.304%   $221.0272   $221.03   $221.05   $221.00  
  Purchase #7 $51.35   7.255%   $55.0754   $55.08   $55.10   $55.10  
  7 purchase totals = $761.66       $837.3704   $837.38   $837.45   $837.40