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 $53.99   6.588%   $57.5469   $57.55   $57.55   $57.50  
  Purchase #2 $165.61   11.334%   $184.3802   $184.38   $184.40   $184.40  
  Purchase #3 $32.53   7.813%   $35.0716   $35.07   $35.05   $35.10  
  Purchase #4 $148.59   12.338%   $166.923   $166.92   $166.90   $166.90  
  Purchase #5 $209.41   7.645%   $225.4194   $225.42   $225.40   $225.40  
  Purchase #6 $140.35   8.122%   $151.7492   $151.75   $151.75   $151.70  
  Purchase #7 $221.58   9.706%   $243.0866   $243.09   $243.10   $243.10  
  7 purchase totals = $972.06       $1,064.1769   $1,064.18   $1,064.15   $1,064.10