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 $239.69   11.231%   $266.6096   $266.61   $266.60   $266.60  
  Purchase #2 $167.53   7.607%   $180.274   $180.27   $180.25   $180.30  
  Purchase #3 $68.81   10.303%   $75.8995   $75.90   $75.90   $75.90  
  Purchase #4 $124.68   7.564%   $134.1108   $134.11   $134.10   $134.10  
  Purchase #5 $50.90   10.374%   $56.1804   $56.18   $56.20   $56.20  
  Purchase #6 $169.57   9.311%   $185.3587   $185.36   $185.35   $185.40  
  Purchase #7 $99.65   12.161%   $111.7684   $111.77   $111.75   $111.80  
  7 purchase totals = $920.83       $1,010.2014   $1,010.20   $1,010.15   $1,010.30