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 $14.93   4.758%   $15.6404   $15.64   $15.65   $15.60  
  Purchase #2 $205.27   4.485%   $214.4764   $214.48   $214.50   $214.50  
  Purchase #3 $59.91   12.258%   $67.2538   $67.25   $67.25   $67.30  
  Purchase #4 $191.47   11.631%   $213.7399   $213.74   $213.75   $213.70  
  Purchase #5 $111.43   9.379%   $121.881   $121.88   $121.90   $121.90  
  Purchase #6 $144.34   11.469%   $160.8944   $160.89   $160.90   $160.90  
  Purchase #7 $236.64   4.588%   $247.497   $247.50   $247.50   $247.50  
  7 purchase totals = $963.99       $1,041.3829   $1,041.38   $1,041.45   $1,041.40