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 $205.76   10.196%   $226.7393   $226.74   $226.75   $226.70  
  Purchase #2 $74.48   6.401%   $79.2475   $79.25   $79.25   $79.20  
  Purchase #3 $177.86   8.586%   $193.1311   $193.13   $193.15   $193.10  
  Purchase #4 $213.55   11.704%   $238.5439   $238.54   $238.55   $238.50  
  Purchase #5 $142.40   11.447%   $158.7005   $158.70   $158.70   $158.70  
  Purchase #6 $73.72   4.565%   $77.0853   $77.09   $77.10   $77.10  
  Purchase #7 $44.38   13.747%   $50.4809   $50.48   $50.50   $50.50  
  7 purchase totals = $932.15       $1,023.9285   $1,023.93   $1,024.00   $1,023.80