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 $62.59   10.750%   $69.3184   $69.32   $69.30   $69.30  
  Purchase #2 $86.30   9.681%   $94.6547   $94.65   $94.65   $94.70  
  Purchase #3 $167.81   5.283%   $176.6754   $176.68   $176.70   $176.70  
  Purchase #4 $248.54   9.308%   $271.6741   $271.67   $271.65   $271.70  
  Purchase #5 $23.91   6.618%   $25.4924   $25.49   $25.50   $25.50  
  Purchase #6 $221.76   12.815%   $250.1785   $250.18   $250.20   $250.20  
  Purchase #7 $12.92   9.543%   $14.153   $14.15   $14.15   $14.20  
  7 purchase totals = $823.83       $902.1465   $902.14   $902.15   $902.30