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 $238.44   13.212%   $269.9427   $269.94   $269.95   $269.90  
  Purchase #2 $127.91   10.173%   $140.9223   $140.92   $140.90   $140.90  
  Purchase #3 $101.44   11.119%   $112.7191   $112.72   $112.70   $112.70  
  Purchase #4 $40.94   5.761%   $43.2986   $43.30   $43.30   $43.30  
  Purchase #5 $237.89   4.273%   $248.055   $248.06   $248.05   $248.10  
  Purchase #6 $69.51   3.551%   $71.9783   $71.98   $72.00   $72.00  
  Purchase #7 $216.75   11.722%   $242.1574   $242.16   $242.15   $242.20  
  7 purchase totals = $1,032.88       $1,129.0734   $1,129.08   $1,129.05   $1,129.10