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 $241.82   11.623%   $269.9267   $269.93   $269.95   $269.90  
  Purchase #2 $56.58   6.616%   $60.3233   $60.32   $60.30   $60.30  
  Purchase #3 $43.67   5.714%   $46.1653   $46.17   $46.15   $46.20  
  Purchase #4 $22.88   8.706%   $24.8719   $24.87   $24.85   $24.90  
  Purchase #5 $99.83   9.794%   $109.6074   $109.61   $109.60   $109.60  
  Purchase #6 $202.98   4.491%   $212.0958   $212.10   $212.10   $212.10  
  Purchase #7 $164.46   13.476%   $186.6226   $186.62   $186.60   $186.60  
  7 purchase totals = $832.22       $909.6130   $909.62   $909.55   $909.60