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 $54.68   12.617%   $61.579   $61.58   $61.60   $61.60  
  Purchase #2 $94.98   10.672%   $105.1163   $105.12   $105.10   $105.10  
  Purchase #3 $59.77   11.193%   $66.4601   $66.46   $66.45   $66.50  
  Purchase #4 $250.31   11.158%   $278.2396   $278.24   $278.25   $278.20  
  Purchase #5 $127.34   9.407%   $139.3189   $139.32   $139.30   $139.30  
  Purchase #6 $82.90   12.176%   $92.9939   $92.99   $93.00   $93.00  
  Purchase #7 $162.76   7.515%   $174.9914   $174.99   $175.00   $175.00  
  7 purchase totals = $832.74       $918.6992   $918.70   $918.70   $918.70