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 $237.81   10.270%   $262.2331   $262.23   $262.25   $262.20  
  Purchase #2 $49.57   6.496%   $52.7901   $52.79   $52.80   $52.80  
  Purchase #3 $23.61   13.212%   $26.7294   $26.73   $26.75   $26.70  
  Purchase #4 $188.78   7.642%   $203.2066   $203.21   $203.20   $203.20  
  Purchase #5 $179.39   9.225%   $195.9387   $195.94   $195.95   $195.90  
  Purchase #6 $44.50   4.671%   $46.5786   $46.58   $46.60   $46.60  
  Purchase #7 $18.44   12.349%   $20.7172   $20.72   $20.70   $20.70  
  7 purchase totals = $742.10       $808.1937   $808.20   $808.25   $808.10