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 $208.96   5.615%   $220.6931   $220.69   $220.70   $220.70  
  Purchase #2 $246.75   6.436%   $262.6308   $262.63   $262.65   $262.60  
  Purchase #3 $11.81   13.488%   $13.4029   $13.40   $13.40   $13.40  
  Purchase #4 $222.32   12.503%   $250.1167   $250.12   $250.10   $250.10  
  Purchase #5 $249.30   9.156%   $272.1259   $272.13   $272.15   $272.10  
  Purchase #6 $142.91   3.387%   $147.7504   $147.75   $147.75   $147.80  
  Purchase #7 $167.61   8.491%   $181.8418   $181.84   $181.85   $181.80  
  7 purchase totals = $1,249.66       $1,348.5616   $1,348.56   $1,348.60   $1,348.50