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 $236.61   11.799%   $264.5276   $264.53   $264.55   $264.50  
  Purchase #2 $183.49   7.546%   $197.3362   $197.34   $197.35   $197.30  
  Purchase #3 $223.71   11.144%   $248.6402   $248.64   $248.65   $248.60  
  Purchase #4 $215.61   9.773%   $236.6816   $236.68   $236.70   $236.70  
  Purchase #5 $206.62   9.722%   $226.7076   $226.71   $226.70   $226.70  
  Purchase #6 $202.99   3.285%   $209.6582   $209.66   $209.65   $209.70  
  Purchase #7 $63.93   13.787%   $72.744   $72.74   $72.75   $72.70  
  7 purchase totals = $1,332.96       $1,456.2954   $1,456.30   $1,456.35   $1,456.20