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 $43.93   10.713%   $48.6362   $48.64   $48.65   $48.60  
  Purchase #2 $200.58   6.704%   $214.0269   $214.03   $214.05   $214.00  
  Purchase #3 $155.52   3.530%   $161.0099   $161.01   $161.00   $161.00  
  Purchase #4 $136.31   4.587%   $142.5625   $142.56   $142.55   $142.60  
  Purchase #5 $37.32   10.525%   $41.2479   $41.25   $41.25   $41.20  
  Purchase #6 $226.70   10.495%   $250.4922   $250.49   $250.50   $250.50  
  Purchase #7 $126.71   13.372%   $143.6537   $143.65   $143.65   $143.70  
  7 purchase totals = $927.07       $1,001.6293   $1,001.63   $1,001.65   $1,001.60