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 $204.63   11.583%   $228.3323   $228.33   $228.35   $228.30  
  Purchase #2 $32.80   10.255%   $36.1636   $36.16   $36.15   $36.20  
  Purchase #3 $241.41   9.182%   $263.5763   $263.58   $263.60   $263.60  
  Purchase #4 $208.64   13.223%   $236.2285   $236.23   $236.25   $236.20  
  Purchase #5 $55.58   12.704%   $62.6409   $62.64   $62.65   $62.60  
  Purchase #6 $156.33   9.594%   $171.3283   $171.33   $171.35   $171.30  
  Purchase #7 $24.53   8.808%   $26.6906   $26.69   $26.70   $26.70  
  7 purchase totals = $923.92       $1,024.9605   $1,024.96   $1,025.05   $1,024.90