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 $58.67   10.147%   $64.6232   $64.62   $64.60   $64.60  
  Purchase #2 $220.35   12.841%   $248.6451   $248.65   $248.65   $248.60  
  Purchase #3 $193.45   11.318%   $215.3447   $215.34   $215.35   $215.30  
  Purchase #4 $7.83   3.461%   $8.101   $8.10   $8.10   $8.10  
  Purchase #5 $180.90   3.241%   $186.763   $186.76   $186.75   $186.80  
  Purchase #6 $80.50   7.485%   $86.5254   $86.53   $86.55   $86.50  
  Purchase #7 $165.80   10.369%   $182.9918   $182.99   $183.00   $183.00  
  7 purchase totals = $907.50       $992.9942   $992.99   $993.00   $992.90