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 $205.99   4.654%   $215.5768   $215.58   $215.60   $215.60  
  Purchase #2 $22.34   4.416%   $23.3265   $23.33   $23.35   $23.30  
  Purchase #3 $242.76   13.309%   $275.0689   $275.07   $275.05   $275.10  
  Purchase #4 $229.55   6.312%   $244.0392   $244.04   $244.05   $244.00  
  Purchase #5 $100.35   9.105%   $109.4869   $109.49   $109.50   $109.50  
  Purchase #6 $171.27   13.218%   $193.9085   $193.91   $193.90   $193.90  
  Purchase #7 $56.90   11.365%   $63.3667   $63.37   $63.35   $63.40  
  7 purchase totals = $1,029.16       $1,124.7735   $1,124.79   $1,124.80   $1,124.80