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 $176.40   5.648%   $186.3631   $186.36   $186.35   $186.40  
  Purchase #2 $175.47   12.464%   $197.3406   $197.34   $197.35   $197.30  
  Purchase #3 $75.97   7.398%   $81.5903   $81.59   $81.60   $81.60  
  Purchase #4 $125.66   7.653%   $135.2768   $135.28   $135.30   $135.30  
  Purchase #5 $33.58   4.258%   $35.0098   $35.01   $35.00   $35.00  
  Purchase #6 $194.61   4.361%   $203.0969   $203.10   $203.10   $203.10  
  Purchase #7 $226.79   4.669%   $237.3788   $237.38   $237.40   $237.40  
  7 purchase totals = $1,008.48       $1,076.0563   $1,076.06   $1,076.10   $1,076.10