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 $60.34   4.859%   $63.2719   $63.27   $63.25   $63.30  
  Purchase #2 $141.71   4.133%   $147.5669   $147.57   $147.55   $147.60  
  Purchase #3 $126.45   4.292%   $131.8772   $131.88   $131.90   $131.90  
  Purchase #4 $231.74   13.810%   $263.7433   $263.74   $263.75   $263.70  
  Purchase #5 $47.59   5.366%   $50.1437   $50.14   $50.15   $50.10  
  Purchase #6 $235.75   11.252%   $262.2766   $262.28   $262.30   $262.30  
  Purchase #7 $133.33   11.583%   $148.7736   $148.77   $148.75   $148.80  
  7 purchase totals = $976.91       $1,067.6532   $1,067.65   $1,067.65   $1,067.70