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 $246.54   5.496%   $260.0898   $260.09   $260.10   $260.10  
  Purchase #2 $225.79   7.128%   $241.8843   $241.88   $241.90   $241.90  
  Purchase #3 $204.47   13.147%   $231.3517   $231.35   $231.35   $231.40  
  Purchase #4 $250.36   4.692%   $262.1069   $262.11   $262.10   $262.10  
  Purchase #5 $41.50   5.182%   $43.6505   $43.65   $43.65   $43.70  
  Purchase #6 $147.94   11.664%   $165.1957   $165.20   $165.20   $165.20  
  Purchase #7 $13.88   11.516%   $15.4784   $15.48   $15.50   $15.50  
  7 purchase totals = $1,130.48       $1,219.7573   $1,219.76   $1,219.80   $1,219.90