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 $218.33   10.580%   $241.4293   $241.43   $241.45   $241.40  
  Purchase #2 $58.46   10.778%   $64.7608   $64.76   $64.75   $64.80  
  Purchase #3 $210.37   11.299%   $234.1397   $234.14   $234.15   $234.10  
  Purchase #4 $226.43   11.218%   $251.8309   $251.83   $251.85   $251.80  
  Purchase #5 $87.89   8.844%   $95.663   $95.66   $95.65   $95.70  
  Purchase #6 $164.85   3.323%   $170.328   $170.33   $170.35   $170.30  
  Purchase #7 $237.43   4.560%   $248.2568   $248.26   $248.25   $248.30  
  7 purchase totals = $1,203.76       $1,306.4085   $1,306.41   $1,306.45   $1,306.40