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 $63.32   3.710%   $65.6692   $65.67   $65.65   $65.70  
  Purchase #2 $113.32   11.271%   $126.0923   $126.09   $126.10   $126.10  
  Purchase #3 $231.76   3.679%   $240.2865   $240.29   $240.30   $240.30  
  Purchase #4 $135.51   8.773%   $147.3983   $147.40   $147.40   $147.40  
  Purchase #5 $42.32   11.667%   $47.2575   $47.26   $47.25   $47.30  
  Purchase #6 $196.35   8.822%   $213.672   $213.67   $213.65   $213.70  
  Purchase #7 $180.79   9.263%   $197.5366   $197.54   $197.55   $197.50  
  7 purchase totals = $963.37       $1,037.9124   $1,037.92   $1,037.90   $1,038.00