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 $222.45   4.636%   $232.7628   $232.76   $232.75   $232.80  
  Purchase #2 $190.84   8.667%   $207.3801   $207.38   $207.40   $207.40  
  Purchase #3 $25.49   8.168%   $27.572   $27.57   $27.55   $27.60  
  Purchase #4 $76.88   4.707%   $80.4987   $80.50   $80.50   $80.50  
  Purchase #5 $67.39   4.423%   $70.3707   $70.37   $70.35   $70.40  
  Purchase #6 $144.50   13.747%   $164.3644   $164.36   $164.35   $164.40  
  Purchase #7 $216.25   10.762%   $239.5228   $239.52   $239.50   $239.50  
  7 purchase totals = $943.80       $1,022.4715   $1,022.46   $1,022.40   $1,022.60