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 $176.97   11.493%   $197.3092   $197.31   $197.30   $197.30  
  Purchase #2 $127.91   8.536%   $138.8284   $138.83   $138.85   $138.80  
  Purchase #3 $152.34   12.834%   $171.8913   $171.89   $171.90   $171.90  
  Purchase #4 $77.93   13.860%   $88.7311   $88.73   $88.75   $88.70  
  Purchase #5 $233.43   6.533%   $248.68   $248.68   $248.70   $248.70  
  Purchase #6 $201.38   11.148%   $223.8298   $223.83   $223.85   $223.80  
  Purchase #7 $175.58   4.569%   $183.6023   $183.60   $183.60   $183.60  
  7 purchase totals = $1,145.54       $1,252.8721   $1,252.87   $1,252.95   $1,252.80