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 $38.92   11.434%   $43.3701   $43.37   $43.35   $43.40  
  Purchase #2 $221.83   11.640%   $247.651   $247.65   $247.65   $247.70  
  Purchase #3 $125.77   11.242%   $139.9091   $139.91   $139.90   $139.90  
  Purchase #4 $171.92   11.438%   $191.5842   $191.58   $191.60   $191.60  
  Purchase #5 $86.54   11.660%   $96.6306   $96.63   $96.65   $96.60  
  Purchase #6 $167.40   4.706%   $175.2778   $175.28   $175.30   $175.30  
  Purchase #7 $71.74   13.750%   $81.6043   $81.60   $81.60   $81.60  
  7 purchase totals = $884.12       $976.0271   $976.02   $976.05   $976.10