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 $184.26   11.358%   $205.1883   $205.19   $205.20   $205.20  
  Purchase #2 $84.47   13.665%   $96.0128   $96.01   $96.00   $96.00  
  Purchase #3 $119.45   3.456%   $123.5782   $123.58   $123.60   $123.60  
  Purchase #4 $74.47   6.448%   $79.2718   $79.27   $79.25   $79.30  
  Purchase #5 $12.94   3.264%   $13.3624   $13.36   $13.35   $13.40  
  Purchase #6 $72.28   5.421%   $76.1983   $76.20   $76.20   $76.20  
  Purchase #7 $179.70   4.358%   $187.5313   $187.53   $187.55   $187.50  
  7 purchase totals = $727.57       $781.1431   $781.14   $781.15   $781.20