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 $54.38   4.242%   $56.6868   $56.69   $56.70   $56.70  
  Purchase #2 $224.85   9.664%   $246.5795   $246.58   $246.60   $246.60  
  Purchase #3 $195.88   6.632%   $208.8708   $208.87   $208.85   $208.90  
  Purchase #4 $125.69   5.237%   $132.2724   $132.27   $132.25   $132.30  
  Purchase #5 $91.39   7.126%   $97.9025   $97.90   $97.90   $97.90  
  Purchase #6 $120.43   12.641%   $135.6536   $135.65   $135.65   $135.70  
  Purchase #7 $178.65   12.691%   $201.3225   $201.32   $201.30   $201.30  
  7 purchase totals = $991.27       $1,079.2881   $1,079.28   $1,079.25   $1,079.40