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 $24.58   9.706%   $26.9657   $26.97   $26.95   $27.00  
  Purchase #2 $217.27   13.135%   $245.8084   $245.81   $245.80   $245.80  
  Purchase #3 $142.98   8.695%   $155.4121   $155.41   $155.40   $155.40  
  Purchase #4 $69.77   6.196%   $74.0929   $74.09   $74.10   $74.10  
  Purchase #5 $55.44   9.201%   $60.541   $60.54   $60.55   $60.50  
  Purchase #6 $199.75   4.341%   $208.4211   $208.42   $208.40   $208.40  
  Purchase #7 $240.27   13.631%   $273.0212   $273.02   $273.00   $273.00  
  7 purchase totals = $950.06       $1,044.2624   $1,044.26   $1,044.20   $1,044.20