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 $63.28   9.635%   $69.377   $69.38   $69.40   $69.40  
  Purchase #2 $90.53   5.692%   $95.683   $95.68   $95.70   $95.70  
  Purchase #3 $215.63   13.759%   $245.2985   $245.30   $245.30   $245.30  
  Purchase #4 $142.58   4.421%   $148.8835   $148.88   $148.90   $148.90  
  Purchase #5 $61.60   12.709%   $69.4287   $69.43   $69.45   $69.40  
  Purchase #6 $218.34   13.444%   $247.6936   $247.69   $247.70   $247.70  
  Purchase #7 $131.95   8.716%   $143.4508   $143.45   $143.45   $143.50  
  7 purchase totals = $923.91       $1,019.8151   $1,019.81   $1,019.90   $1,019.90