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 $172.75   11.170%   $192.0462   $192.05   $192.05   $192.00  
  Purchase #2 $118.62   11.704%   $132.5033   $132.50   $132.50   $132.50  
  Purchase #3 $32.81   4.769%   $34.3747   $34.37   $34.35   $34.40  
  Purchase #4 $241.61   3.755%   $250.6825   $250.68   $250.70   $250.70  
  Purchase #5 $225.76   9.850%   $247.9974   $248.00   $248.00   $248.00  
  Purchase #6 $222.65   5.541%   $234.987   $234.99   $235.00   $235.00  
  Purchase #7 $164.95   5.252%   $173.6132   $173.61   $173.60   $173.60  
  7 purchase totals = $1,179.15       $1,266.2043   $1,266.20   $1,266.20   $1,266.20