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 $144.61   5.767%   $152.9497   $152.95   $152.95   $152.90  
  Purchase #2 $226.47   11.509%   $252.5344   $252.53   $252.55   $252.50  
  Purchase #3 $232.28   3.258%   $239.8477   $239.85   $239.85   $239.80  
  Purchase #4 $30.40   7.309%   $32.6219   $32.62   $32.60   $32.60  
  Purchase #5 $142.52   8.402%   $154.4945   $154.49   $154.50   $154.50  
  Purchase #6 $98.67   10.551%   $109.0807   $109.08   $109.10   $109.10  
  Purchase #7 $79.60   8.441%   $86.319   $86.32   $86.30   $86.30  
  7 purchase totals = $954.55       $1,027.8479   $1,027.84   $1,027.85   $1,027.70