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 $114.64   8.184%   $124.0221   $124.02   $124.00   $124.00  
  Purchase #2 $182.79   7.605%   $196.6912   $196.69   $196.70   $196.70  
  Purchase #3 $54.94   8.447%   $59.5808   $59.58   $59.60   $59.60  
  Purchase #4 $89.62   9.329%   $97.9806   $97.98   $98.00   $98.00  
  Purchase #5 $211.40   5.170%   $222.3294   $222.33   $222.35   $222.30  
  Purchase #6 $75.49   8.185%   $81.6689   $81.67   $81.65   $81.70  
  Purchase #7 $73.93   4.296%   $77.106   $77.11   $77.10   $77.10  
  7 purchase totals = $802.81       $859.3790   $859.38   $859.40   $859.40