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 $42.70   11.553%   $47.6331   $47.63   $47.65   $47.60  
  Purchase #2 $63.41   5.145%   $66.6724   $66.67   $66.65   $66.70  
  Purchase #3 $165.64   3.798%   $171.931   $171.93   $171.95   $171.90  
  Purchase #4 $79.90   7.773%   $86.1106   $86.11   $86.10   $86.10  
  Purchase #5 $163.57   7.329%   $175.558   $175.56   $175.55   $175.60  
  Purchase #6 $117.57   12.665%   $132.4602   $132.46   $132.45   $132.50  
  Purchase #7 $70.43   8.457%   $76.3863   $76.39   $76.40   $76.40  
  7 purchase totals = $703.22       $756.7516   $756.75   $756.75   $756.80