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 $153.93   12.571%   $173.2805   $173.28   $173.30   $173.30  
  Purchase #2 $49.56   6.112%   $52.5891   $52.59   $52.60   $52.60  
  Purchase #3 $226.86   11.737%   $253.4866   $253.49   $253.50   $253.50  
  Purchase #4 $190.73   5.687%   $201.5768   $201.58   $201.60   $201.60  
  Purchase #5 $159.93   10.365%   $176.5067   $176.51   $176.50   $176.50  
  Purchase #6 $242.76   9.509%   $265.844   $265.84   $265.85   $265.80  
  Purchase #7 $71.82   11.725%   $80.2409   $80.24   $80.25   $80.20  
  7 purchase totals = $1,095.59       $1,203.5246   $1,203.53   $1,203.60   $1,203.50