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 $86.40   11.276%   $96.1425   $96.14   $96.15   $96.10  
  Purchase #2 $178.76   8.794%   $194.4802   $194.48   $194.50   $194.50  
  Purchase #3 $53.35   5.486%   $56.2768   $56.28   $56.30   $56.30  
  Purchase #4 $74.79   13.302%   $84.7386   $84.74   $84.75   $84.70  
  Purchase #5 $207.66   12.805%   $234.2509   $234.25   $234.25   $234.30  
  Purchase #6 $41.86   12.630%   $47.1469   $47.15   $47.15   $47.10  
  Purchase #7 $229.46   5.350%   $241.7361   $241.74   $241.75   $241.70  
  7 purchase totals = $872.28       $954.7720   $954.78   $954.85   $954.70