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 $241.79   11.260%   $269.0156   $269.02   $269.00   $269.00  
  Purchase #2 $159.79   13.348%   $181.1188   $181.12   $181.10   $181.10  
  Purchase #3 $86.83   12.841%   $97.9798   $97.98   $98.00   $98.00  
  Purchase #4 $188.35   10.478%   $208.0853   $208.09   $208.10   $208.10  
  Purchase #5 $143.94   6.431%   $153.1968   $153.20   $153.20   $153.20  
  Purchase #6 $242.32   4.166%   $252.4151   $252.42   $252.40   $252.40  
  Purchase #7 $157.94   10.800%   $174.9975   $175.00   $175.00   $175.00  
  7 purchase totals = $1,220.96       $1,336.8089   $1,336.83   $1,336.80   $1,336.80