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 $61.44   8.675%   $66.7699   $66.77   $66.75   $66.80  
  Purchase #2 $199.25   7.743%   $214.6779   $214.68   $214.70   $214.70  
  Purchase #3 $117.75   11.373%   $131.1417   $131.14   $131.15   $131.10  
  Purchase #4 $127.80   4.374%   $133.39   $133.39   $133.40   $133.40  
  Purchase #5 $64.84   8.456%   $70.3229   $70.32   $70.30   $70.30  
  Purchase #6 $201.26   11.784%   $224.9765   $224.98   $225.00   $225.00  
  Purchase #7 $111.49   9.869%   $122.4929   $122.49   $122.50   $122.50  
  7 purchase totals = $883.83       $963.7718   $963.77   $963.80   $963.80