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 $168.43   13.749%   $191.5874   $191.59   $191.60   $191.60  
  Purchase #2 $145.40   11.128%   $161.5801   $161.58   $161.60   $161.60  
  Purchase #3 $241.27   8.512%   $261.8069   $261.81   $261.80   $261.80  
  Purchase #4 $167.36   8.116%   $180.9429   $180.94   $180.95   $180.90  
  Purchase #5 $245.67   5.418%   $258.9804   $258.98   $259.00   $259.00  
  Purchase #6 $227.70   7.607%   $245.0211   $245.02   $245.00   $245.00  
  Purchase #7 $24.65   11.777%   $27.553   $27.55   $27.55   $27.60  
  7 purchase totals = $1,220.48       $1,327.4718   $1,327.47   $1,327.50   $1,327.50