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 $149.33   8.871%   $162.5771   $162.58   $162.60   $162.60  
  Purchase #2 $15.76   9.247%   $17.2173   $17.22   $17.20   $17.20  
  Purchase #3 $160.54   12.239%   $180.1885   $180.19   $180.20   $180.20  
  Purchase #4 $111.82   3.807%   $116.077   $116.08   $116.10   $116.10  
  Purchase #5 $208.39   10.699%   $230.6856   $230.69   $230.70   $230.70  
  Purchase #6 $51.30   10.404%   $56.6373   $56.64   $56.65   $56.60  
  Purchase #7 $228.72   3.555%   $236.851   $236.85   $236.85   $236.90  
  7 purchase totals = $925.86       $1,000.2338   $1,000.25   $1,000.30   $1,000.30