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 $58.25   11.824%   $65.1375   $65.14   $65.15   $65.10  
  Purchase #2 $192.89   7.157%   $206.6951   $206.70   $206.70   $206.70  
  Purchase #3 $112.92   11.829%   $126.2773   $126.28   $126.30   $126.30  
  Purchase #4 $65.35   9.821%   $71.768   $71.77   $71.75   $71.80  
  Purchase #5 $56.68   9.382%   $61.9977   $62.00   $62.00   $62.00  
  Purchase #6 $61.76   9.511%   $67.634   $67.63   $67.65   $67.60  
  Purchase #7 $164.83   3.584%   $170.7375   $170.74   $170.75   $170.70  
  7 purchase totals = $712.68       $770.2471   $770.26   $770.30   $770.20