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 $192.35   8.426%   $208.5574   $208.56   $208.55   $208.60  
  Purchase #2 $169.50   9.510%   $185.6195   $185.62   $185.60   $185.60  
  Purchase #3 $33.62   5.347%   $35.4177   $35.42   $35.40   $35.40  
  Purchase #4 $120.73   7.865%   $130.2254   $130.23   $130.25   $130.20  
  Purchase #5 $53.98   3.334%   $55.7797   $55.78   $55.80   $55.80  
  Purchase #6 $66.30   3.459%   $68.5933   $68.59   $68.60   $68.60  
  Purchase #7 $235.40   13.751%   $267.7699   $267.77   $267.75   $267.80  
  7 purchase totals = $871.88       $951.9629   $951.97   $951.95   $952.00