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 $47.51   8.588%   $51.5902   $51.59   $51.60   $51.60  
  Purchase #2 $129.46   7.183%   $138.7591   $138.76   $138.75   $138.80  
  Purchase #3 $148.96   3.861%   $154.7113   $154.71   $154.70   $154.70  
  Purchase #4 $246.53   6.210%   $261.8395   $261.84   $261.85   $261.80  
  Purchase #5 $97.80   11.721%   $109.2631   $109.26   $109.25   $109.30  
  Purchase #6 $244.36   8.371%   $264.8154   $264.82   $264.80   $264.80  
  Purchase #7 $49.61   13.696%   $56.4046   $56.40   $56.40   $56.40  
  7 purchase totals = $964.23       $1,037.3832   $1,037.38   $1,037.35   $1,037.40