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 $58.99   11.493%   $65.7697   $65.77   $65.75   $65.80  
  Purchase #2 $54.93   11.872%   $61.4513   $61.45   $61.45   $61.50  
  Purchase #3 $117.42   12.442%   $132.0294   $132.03   $132.05   $132.00  
  Purchase #4 $220.90   5.402%   $232.833   $232.83   $232.85   $232.80  
  Purchase #5 $26.41   3.348%   $27.2942   $27.29   $27.30   $27.30  
  Purchase #6 $114.82   10.800%   $127.2206   $127.22   $127.20   $127.20  
  Purchase #7 $82.44   7.525%   $88.6436   $88.64   $88.65   $88.60  
  7 purchase totals = $675.91       $735.2418   $735.23   $735.25   $735.20