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 $37.86   13.724%   $43.0559   $43.06   $43.05   $43.10  
  Purchase #2 $226.27   10.579%   $250.2071   $250.21   $250.20   $250.20  
  Purchase #3 $165.41   5.490%   $174.491   $174.49   $174.50   $174.50  
  Purchase #4 $71.93   5.393%   $75.8092   $75.81   $75.80   $75.80  
  Purchase #5 $169.45   3.536%   $175.4418   $175.44   $175.45   $175.40  
  Purchase #6 $85.75   12.239%   $96.2449   $96.24   $96.25   $96.20  
  Purchase #7 $233.78   9.131%   $255.1265   $255.13   $255.15   $255.10  
  7 purchase totals = $990.45       $1,070.3764   $1,070.38   $1,070.40   $1,070.30