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 $241.61   10.201%   $266.2566   $266.26   $266.25   $266.30  
  Purchase #2 $52.88   6.683%   $56.414   $56.41   $56.40   $56.40  
  Purchase #3 $202.83   7.540%   $218.1234   $218.12   $218.10   $218.10  
  Purchase #4 $59.88   3.121%   $61.7489   $61.75   $61.75   $61.70  
  Purchase #5 $110.25   5.239%   $116.026   $116.03   $116.05   $116.00  
  Purchase #6 $87.53   11.293%   $97.4148   $97.41   $97.40   $97.40  
  Purchase #7 $45.95   11.693%   $51.3229   $51.32   $51.30   $51.30  
  7 purchase totals = $800.93       $867.3066   $867.30   $867.25   $867.20