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 $118.91   13.293%   $134.7167   $134.72   $134.70   $134.70  
  Purchase #2 $179.77   3.161%   $185.4525   $185.45   $185.45   $185.50  
  Purchase #3 $83.74   8.300%   $90.6904   $90.69   $90.70   $90.70  
  Purchase #4 $235.96   12.121%   $264.5607   $264.56   $264.55   $264.60  
  Purchase #5 $236.51   5.139%   $248.6642   $248.66   $248.65   $248.70  
  Purchase #6 $188.77   4.874%   $197.9706   $197.97   $197.95   $198.00  
  Purchase #7 $101.31   11.195%   $112.6517   $112.65   $112.65   $112.70  
  7 purchase totals = $1,144.97       $1,234.7068   $1,234.70   $1,234.65   $1,234.90