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 $176.98   5.115%   $186.0325   $186.03   $186.05   $186.00  
  Purchase #2 $186.69   5.186%   $196.3717   $196.37   $196.35   $196.40  
  Purchase #3 $38.61   8.557%   $41.9139   $41.91   $41.90   $41.90  
  Purchase #4 $233.35   12.295%   $262.0404   $262.04   $262.05   $262.00  
  Purchase #5 $107.80   9.397%   $117.93   $117.93   $117.95   $117.90  
  Purchase #6 $152.75   9.601%   $167.4155   $167.42   $167.40   $167.40  
  Purchase #7 $243.78   6.102%   $258.6555   $258.66   $258.65   $258.70  
  7 purchase totals = $1,139.96       $1,230.3595   $1,230.36   $1,230.35   $1,230.30