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 $239.61   9.458%   $262.2723   $262.27   $262.25   $262.30  
  Purchase #2 $55.69   5.828%   $58.9356   $58.94   $58.95   $58.90  
  Purchase #3 $63.56   9.184%   $69.3974   $69.40   $69.40   $69.40  
  Purchase #4 $194.87   11.249%   $216.7909   $216.79   $216.80   $216.80  
  Purchase #5 $206.25   13.476%   $234.0443   $234.04   $234.05   $234.00  
  Purchase #6 $153.40   6.816%   $163.8557   $163.86   $163.85   $163.90  
  Purchase #7 $104.47   7.283%   $112.0786   $112.08   $112.10   $112.10  
  7 purchase totals = $1,017.85       $1,117.3748   $1,117.38   $1,117.40   $1,117.40