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 $103.61   3.830%   $107.5783   $107.58   $107.60   $107.60  
  Purchase #2 $230.75   4.281%   $240.6284   $240.63   $240.65   $240.60  
  Purchase #3 $208.81   3.294%   $215.6882   $215.69   $215.70   $215.70  
  Purchase #4 $147.27   11.117%   $163.642   $163.64   $163.65   $163.60  
  Purchase #5 $95.96   7.725%   $103.3729   $103.37   $103.35   $103.40  
  Purchase #6 $164.73   9.691%   $180.694   $180.69   $180.70   $180.70  
  Purchase #7 $84.94   11.333%   $94.5663   $94.57   $94.55   $94.60  
  7 purchase totals = $1,036.07       $1,106.1701   $1,106.17   $1,106.20   $1,106.20