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 $54.35   8.631%   $59.0409   $59.04   $59.05   $59.00  
  Purchase #2 $129.47   5.241%   $136.2555   $136.26   $136.25   $136.30  
  Purchase #3 $120.66   4.806%   $126.4589   $126.46   $126.45   $126.50  
  Purchase #4 $20.81   13.192%   $23.5553   $23.56   $23.55   $23.60  
  Purchase #5 $103.73   10.381%   $114.4982   $114.50   $114.50   $114.50  
  Purchase #6 $200.57   9.396%   $219.4156   $219.42   $219.40   $219.40  
  Purchase #7 $182.71   13.196%   $206.8204   $206.82   $206.80   $206.80  
  7 purchase totals = $812.30       $886.0448   $886.06   $886.00   $886.10