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 $72.74   6.156%   $77.2179   $77.22   $77.20   $77.20  
  Purchase #2 $247.28   11.329%   $275.2944   $275.29   $275.30   $275.30  
  Purchase #3 $197.43   10.493%   $218.1463   $218.15   $218.15   $218.10  
  Purchase #4 $90.58   8.608%   $98.3771   $98.38   $98.40   $98.40  
  Purchase #5 $205.82   8.427%   $223.1645   $223.16   $223.15   $223.20  
  Purchase #6 $233.88   8.637%   $254.0802   $254.08   $254.10   $254.10  
  Purchase #7 $239.71   3.702%   $248.5841   $248.58   $248.60   $248.60  
  7 purchase totals = $1,287.44       $1,394.8645   $1,394.86   $1,394.90   $1,394.90