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 $216.72   6.814%   $231.4873   $231.49   $231.50   $231.50  
  Purchase #2 $231.29   13.681%   $262.9328   $262.93   $262.95   $262.90  
  Purchase #3 $34.65   4.547%   $36.2255   $36.23   $36.25   $36.20  
  Purchase #4 $188.54   6.605%   $200.9931   $200.99   $201.00   $201.00  
  Purchase #5 $114.79   5.671%   $121.2997   $121.30   $121.30   $121.30  
  Purchase #6 $86.30   6.315%   $91.7498   $91.75   $91.75   $91.70  
  Purchase #7 $64.58   3.386%   $66.7667   $66.77   $66.75   $66.80  
  7 purchase totals = $936.87       $1,011.4549   $1,011.46   $1,011.50   $1,011.40