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 $48.53   13.227%   $54.9491   $54.95   $54.95   $54.90  
  Purchase #2 $226.56   11.328%   $252.2247   $252.22   $252.20   $252.20  
  Purchase #3 $158.85   11.326%   $176.8414   $176.84   $176.85   $176.80  
  Purchase #4 $163.43   7.243%   $175.2672   $175.27   $175.25   $175.30  
  Purchase #5 $127.88   7.332%   $137.2562   $137.26   $137.25   $137.30  
  Purchase #6 $107.56   10.564%   $118.9226   $118.92   $118.90   $118.90  
  Purchase #7 $237.38   6.135%   $251.9433   $251.94   $251.95   $251.90  
  7 purchase totals = $1,070.19       $1,167.4045   $1,167.40   $1,167.35   $1,167.30