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 $167.28   3.435%   $173.0261   $173.03   $173.05   $173.00  
  Purchase #2 $170.96   8.610%   $185.6797   $185.68   $185.70   $185.70  
  Purchase #3 $230.76   7.209%   $247.3955   $247.40   $247.40   $247.40  
  Purchase #4 $26.27   3.815%   $27.2722   $27.27   $27.25   $27.30  
  Purchase #5 $30.56   13.381%   $34.6492   $34.65   $34.65   $34.60  
  Purchase #6 $174.35   5.493%   $183.927   $183.93   $183.95   $183.90  
  Purchase #7 $165.45   3.769%   $171.6858   $171.69   $171.70   $171.70  
  7 purchase totals = $965.63       $1,023.6355   $1,023.65   $1,023.70   $1,023.60