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 $58.61   7.171%   $62.8129   $62.81   $62.80   $62.80  
  Purchase #2 $219.26   13.277%   $248.3712   $248.37   $248.35   $248.40  
  Purchase #3 $15.84   6.860%   $16.9266   $16.93   $16.95   $16.90  
  Purchase #4 $32.93   3.225%   $33.992   $33.99   $34.00   $34.00  
  Purchase #5 $107.56   12.464%   $120.9663   $120.97   $120.95   $121.00  
  Purchase #6 $22.84   8.625%   $24.81   $24.81   $24.80   $24.80  
  Purchase #7 $222.28   5.405%   $234.2942   $234.29   $234.30   $234.30  
  7 purchase totals = $679.32       $742.1732   $742.17   $742.15   $742.20