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 $56.93   8.427%   $61.7275   $61.73   $61.75   $61.70  
  Purchase #2 $242.31   11.294%   $269.6765   $269.68   $269.70   $269.70  
  Purchase #3 $98.93   9.587%   $108.4144   $108.41   $108.40   $108.40  
  Purchase #4 $182.82   6.232%   $194.2133   $194.21   $194.20   $194.20  
  Purchase #5 $240.64   3.849%   $249.9022   $249.90   $249.90   $249.90  
  Purchase #6 $49.47   13.374%   $56.0861   $56.09   $56.10   $56.10  
  Purchase #7 $86.62   11.193%   $96.3154   $96.32   $96.30   $96.30  
  7 purchase totals = $957.72       $1,036.3354   $1,036.34   $1,036.35   $1,036.30