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 $57.71   6.305%   $61.3486   $61.35   $61.35   $61.30  
  Purchase #2 $157.86   12.860%   $178.1608   $178.16   $178.15   $178.20  
  Purchase #3 $191.68   7.746%   $206.5275   $206.53   $206.55   $206.50  
  Purchase #4 $30.72   10.153%   $33.839   $33.84   $33.85   $33.80  
  Purchase #5 $101.85   12.518%   $114.5996   $114.60   $114.60   $114.60  
  Purchase #6 $157.73   11.324%   $175.5913   $175.59   $175.60   $175.60  
  Purchase #7 $16.92   3.457%   $17.5049   $17.50   $17.50   $17.50  
  7 purchase totals = $714.47       $787.5717   $787.57   $787.60   $787.50