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 $57.82   3.184%   $59.661   $59.66   $59.65   $59.70  
  Purchase #2 $38.93   4.670%   $40.748   $40.75   $40.75   $40.70  
  Purchase #3 $71.65   4.223%   $74.6758   $74.68   $74.70   $74.70  
  Purchase #4 $187.42   3.288%   $193.5824   $193.58   $193.60   $193.60  
  Purchase #5 $26.57   6.182%   $28.2126   $28.21   $28.20   $28.20  
  Purchase #6 $181.83   6.105%   $192.9307   $192.93   $192.95   $192.90  
  Purchase #7 $227.53   6.701%   $242.7768   $242.78   $242.80   $242.80  
  7 purchase totals = $791.75       $832.5873   $832.59   $832.65   $832.60