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 $222.89   11.859%   $249.3225   $249.32   $249.30   $249.30  
  Purchase #2 $154.50   13.210%   $174.9095   $174.91   $174.90   $174.90  
  Purchase #3 $205.26   5.409%   $216.3625   $216.36   $216.35   $216.40  
  Purchase #4 $167.47   4.343%   $174.7432   $174.74   $174.75   $174.70  
  Purchase #5 $191.62   11.184%   $213.0508   $213.05   $213.05   $213.10  
  Purchase #6 $229.46   3.405%   $237.2731   $237.27   $237.25   $237.30  
  Purchase #7 $220.51   12.336%   $247.7121   $247.71   $247.70   $247.70  
  7 purchase totals = $1,391.71       $1,513.3737   $1,513.36   $1,513.30   $1,513.40